Apparatus and methods for controlling a welding process

ABSTRACT

A method and apparatus for illuminating a weld line wherein a beam of light is directed onto a weld electrode and is reflected off of the electrode, thereby illuminating an area of the weld joint. Also disclosed are an apparatus for detecting a weld line using light from a low power arc which does not form a molten pool and a method and apparatus for locating a weld line by analyzing light reflected from a weld pool.

This is a division of application Ser. No. 853,233, filed Apr. 17, 1986,which is a division of application Ser. No. 436,026 filed Oct. 22, 1982,now U.S. Pat. No. 4,532,408; Ser. No. 456,278 filed Jan. 6, 1983, nowabandoned; and Ser. No. 603,296, filed Apr. 23, 1984, now U.S. Pat. No.4,595,820.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus and method for controlling awelding process. More specifically, the invention relates to apparatusand methods for viewing a welding operation, determining the width of aweld pool, for controlling an arc welding process (including control ofweld penetration) and for locating a weld line. The invention alsorelates to certain data handling techniques which are useful in theinstant welding control process but which may also be useful in otherapplications.

The term "weld line" is used herein to mean the line between theadjacent edges of two metal portions in a weld joint preparation. Thus,the weld line is the line which the welding apparatus should followduring the welding operation. Those skilled in the art will appreciatethat, in some types of weld joint preparations, there will be a gap offinite width between the metal portions being welded and thus the weldline will in fact be a narrow strip rather than a line in the strictmathematical sense of that term. The term "weld joint preparation" isused herein to denote the two metal portions lying adjacent one anotherin a position ready for welding.

The process of arc welding is one of the most widely used manufacturingprocesses in the world. Great efforts have been made in recent years toautomate the welding process in order to allow the use of robot welderswhich are capable of producing very uniform, high quality welds. Suchautomation has the potential both to increase productivity by increasingthe speed and accuracy of the welding process in routine weldingapplications, and to increase the quality of the welds thus produced,thereby allowing automated welding to be utilized in high qualitycontrol industries such as the nuclear power and pressure vesselmanufacturing industries.

In order to develop automatic control of the arc welding process,numerous attempts have been made to determine which are the relevantparameters in the welding process. It has truly been said that only thewelding operator truly knows the quality of the weld and what ishappening in the welding process because only he has hitherto been ableto see precisely the quality of the weld and the physical parameters ofweld pool size and arc length. Also, only the operator has been in aposition to accurately track weld lines which are often irregular inshape.

In recent years, use of television based direct monitoring hasincreased. All prior art television monitoring methods have positionedthe camera so as to provide an oblique view of the weld similar to thatseen by an operator. Unfortunately, such an oblique view inherentlyincludes the electric arc, which is very bright and thus tends to "washout" the entire television picture unless appropriate filters areutilized. Therefore, these prior art methods have required filtering thelight reaching the camera so that only light within a narrow band, or ofseveral discrete wavelengths, reaches the camera, rather than allowingthe camera to receive light of the broad range of wavelengths emitted bythe arc.

Additional problems in obliquely viewing the weld area with a televisionmonitoring camera are that unforeseen obstructions of the view seen bythe camera can arise in real life welding situations can arise. Suchobstructions can be caused by the weld line geometry and by constraintson the placement of the camera. Also, distortion of the image of theweld pool is caused by the oblique viewing position due to parallaxeffects.

Prior art weld pool monitoring techniques such as those alreadydiscussed have been used for a variety of purposes. One such purpose isthe monitoring of weld pool width. Prior methods of analysis of videodata received from viewing the weld pool area with a television camerahave made the assumption that the bright areas represent the weld pooland that once the light intensity has decreased to a certain value, thenthe edge of the weld pool has been reached. Such methods then employ a"go/no-go" type of binary logic system to establish the weld pool width.Unfortunately, there are oscillations in the weld pool caused byfluctuations in the welding current, and also caused by the motion ofthe electrode along the weld line. Such oscillatory motions cause thearea of brightness to appear larger than it actually is. Attempts tomitigate the data error caused by the oscillatory motions have beeneffected simply by correcting the data rather than actual measurementand evaluation of the true weld pool edges.

A further purpose to be served by the weld pool monitoring techniquesalready discussed is to control penetration of the weld i.e. the depthof the melted zone of the weld. It is known that there is a relationshipbetween the width of the weld pool and the penetration achieved by thewelding process and thus it has been thought desirable to be able tomeasure and control weld pool width to effect correspondingly precisecontrol of the penetration being achieved. In order to provide a weld ofadequate strength, weld penetration must be an appropriate percentage ofmetal thickness to produce proper adhesion of the two metal portionsforming the weld joint preparation when the molten metal of the weldpool has resolidified. Full penetration welds are welds in which thepenetration extends all the way through the metal portions. Morecommonly, only partial weld penetration is necessary. However, hithertothe only methods of measuring partial weld penetration have beenintelligent guesswork by an experienced operator or destructive testingtechniques following welding. Such destructive testing techniquesinvolve making a sample weld, cutting a cross-section therethrough andactually measuring the weld penetration. Although recently attempts havebeen made to use non-destructive testing techniques, such as ultrasonicand radiographic analysis, to measure weld penetration, most methods ofnon-destructive testing yield inconclusive results when applied to apartial penetration weld, and thus such non-destructive testingtechniques are usually only used for analysis of full penetration welds.Because of the difficulty of estimating the penetration of partialpenetration welds, engineers have mandated full penetration welds whenthey are concerned about the structural integrity of the final weldedproduct, even though, if proper control of weld penetration could beachieved, only partial penetration welds of specified penetration couldbe used, thereby increasing the speed and efficiency of the weldingprocess while still allowing close design control. There is thus a needfor a method of measuring weld penetration during welding.

A further problem with prior art methods for controlling weldingprocesses is that, if they incorporate computerized analysis of videodata, they tend to make excessive demands upon the capacity and/or speedof memory devices used to handle the video data to be analyzed. Storageof every complete frame of video data received from a typical videocamera presents extreme difficulty both as to the capacity and speed ofthe memory required. For example, storing a typical video frame, usingan eight-bit graytone scale, requires approximately 4 million bits ofinformation per frame, and such frames may be arriving at, typically, 25Hz. One technique for reducing data storage requirements is only tostore the idea of each frame which is of interest, but if this is to bedone it is necessary to allow ready variation of the "window" selectedfor data storage if the analysis method is to be sufficiently flexible.Also, there is the problem that the rate at which video data fromindividual pixels of the image to be analyzed is received by memory maybe quicker than the memory can handle such data, and to overcome thisproblem it is desirable to provide a method whereby a stream of databeing fed to a memory at a higher rate can be split among a plurality ofrelatively slow memories each individually incapable of handling andstoring the incoming stream of data.

Finally, in an automated welding process it is necessary to ensure thatthe welding apparatus accurately tracks the weld line. Attempts havebeen made to track weld lines by means of sensors which look at the lineahead of the welding torch. Such sensors attempt to locate the positionof the weld line relative to the torch and adjust the movement of thewelding torch so that it tracks the weld line. Such methods haveutilized both direct contact type sensors which are "dragged" along theweld line ahead of the welding torch and non-contact sensors such asinfra-red detectors.

In prior art systems for tracking weld lines, in order to avoid damageto the sensor and also to keep the sensor from being obscured by thelight from the arc area, it has been necessary to sense the preparationsome finite distance ahead of the weld torch. This immediately producesthe requirement of having some delay in system response so that in factthe system responds to seam tracking changes at the time when thewelding head is over the area of change, not just as they are sensed.

Prior art weld line tracking devices are of two types. The first typesenses voltage and current variations in the arc when various surfacefeatures of the base metal being welded are encountered. One such systemoscillates the arc back and forth across the weld line noting thevoltage changes due to arc length, the arc length becoming longer as itcrosses the weld line. Various schemes have been proposed to measurethis voltage oscillation; both magnetic and mechanical motion deviceshave previously been utilized. The second type identifies the edges ofthe metal positions on either side of the weld line by analysis of lightfrom the arc reflected off these edges. A feedback system is thenprovided to respond to the reflected light to produce the desired effectof following the weld line. Of course, since the light source is the arcitself, the welding process is already occurring at the weld line andthe system simply keeps the welding torch over the weld line. Since thistype of system tracks the weld line by viewing the line ahead of thewelding torch, means must be provided to delay implementation of anynecessary changes in movement of the welding torch until the torchreaches the appropriate part of the weld line. Also, any process controldata produced by such apparatus are subject to error due to parallaxfrom the oblique camera position, as already described, and theapparatus suffers from the problem that the far side of the weld pool ishidden by the arc itself.

Additionally, when prior art methods for tracking a weld line indicate achange in direction of the weld line, the entire welding assemblyincluding the tracking device and torch must be reoriented so that thetracking device leads the welding torch at all times. Such a systeminherently complicates the weld tracking control system since the torchmust not only be translated to follow the weld line, but it must also berotated so that the tracking device leads the torch head.

Therefore, there is a need for an improved weld line tracking apparatusand method that reduces the delay time between receiving a response andactually moving the torch head. Additionally there is a need for asystem which will allow simple rectilinear translation of the torch headwithout the necessity of also rotating the torch head and trackingdevice.

This invention seeks to provide apparatus and methods for overcoming theaforementioned problems in controlling welding processes.

SUMMARY OF THE INVENTION

Accordingly, this invention provides a method for storing video datacomprising placing in a video-computer interface location data definingthe selected area of a video frame for which video data are to bestored; supplying video data to the video-computer interface; causingthe video-computer interface to identify the beginning of a frame of thevide data; and storing the data from the selected area of the frame asit is supplied to the video-computer interface.

This invention also provides apparatus for storing video data comprisingan input for the video data, location data receiving means receivinglocation data defining a selected area of the video frame for which thevideo data is to be stored, identification means for determining thebeginning of a frame of the video data, and memory means for storingvideo data. This apparatus also includes switching means arranged tostore in the memory means video data supplied to the input when thevideo data relate to pixels lying within the selected area but not tostore in the memory means video data when this video data relates topixels lying outside the selected area.

This invention also provides a memory assembly comprising first andsecond memory means, first and second latch means associated with thefirst and second memory means respectively, and a data input. The memoryassembly also comprises control means for latching a first portion ofdata received at the input on the first latch means, latching a secondand later portion of data received at the input on the second latchmeans, and transferring the first and second portions of data from thefirst and second latch means respectively to the first and second memorymeans respectively.

This invention also provides a method of storing, in a memory assemblycomprising first and second memory means, a stream of data supplied tothe assembly faster than the rate at which the data can be stored ineither of the memories alone. In this method, a first portion of data isreceived and latched on a latching means, a second and subsequent secondportion of data is received and stored in the second memory means, andthe first portion of data is transferred from the latching means to thefirst memory means while the second portion of data is being receivedand stored.

This invention also provides a method for controlling an arc weldingprocess in which a light-generating arc is established between a weldingelectrode (this electrode having an axis) and a weld joint preparation,thereby forming a molten weld pool on the weld joint preparation andcausing light generated by the arc to be reflected from the weld pooland the solid metal surrounding the weld pool. Rays of this reflectedlight travelling substantially parallel to the axis of the electrode arecollected in a video camera and the video output from this camera is fedto a vide monitor, thereby forming on this monitor an image of the weldpool in which the arc is obscured by the electrode. The welding processis then manually controlled using the image displayed on the videomonitor. (This method may hereinafter be referred to as the "manualcontrol method" of the invention.)

This invention also provides a method of measuring the width of a moltenweld pool in an arc welding process in which a light-generating arc isestablished between a welding electrode (this electrode having an axis)and a weld joint preparation, thereby forming the molten weld pool onthe weld joint preparation and causing light generated by the arc to bereflected from the weld pool and the solid metal surrounding the weldpool. Rays of this reflected light travelling substantially parallel tothe axis of the electrode are collected and the light thus collected isanalyzed to locate two local minima of light intensity indicating theedge of the weld pool, these two local minima being located on points onthe periphery of the weld pool spaced from one another. The distancebetween the two local minima is determined, hence determining the widthof the weld pool. (This method may hereinafter be referred to as the"weld pool width measuring method" of the invention).

This invention also provides a process for controlling an arc weldingprocess in which a weld is begun by providing electrical current to forman arc between a welding electrode and a base metal to form a weld poolof liquid metal on the base metal. The natural frequency of oscillationof the pool is measured and the mass of the pool computed from thisfrequency of oscillation. The position of the first edge of the weldpool is determined by analyzing light deflected from the surface of thepool and the adjacent base metal in a direction parallel to butnon-coincident with the axis of the welding electrode for a first locallight intensity minimum. The position of a second edge of the weld poolis determined in a similar manner and the distance between the first andsecond edges is used to determine the width of the pool. The electricalcurrent supplied to the arc welding process is adjusted in response tothe computed mass and width to maintain a constant pool mass and aconstant width between the first and second pool edges.

This invention also provides a method for measuring the mass of a weldpool in an arc welding process in which an electrical current forms anarc from an electrode to the weld pool and an electrical voltage existsacross the arc. In this method the electrical current through the arc isadjusted to a base level, pulsed to a level substantially different fromthis base level, and then returned to its base level, thereby inducingoscillations in the pool. The natural frequency of oscillation of theweld pool is measured after the current has been returned to its baselevel, and finally a value representative of the mass of weld pool isdisplayed in humanly perceptible form. (This method and that describedin the preceding paragraph may hereinafter be referred to as the "weldpool oscillation methods" of the invention.)

This invention also provides a method for controlling the mass of a weldpool in an arc welding process in which an electrical current forms anarc from an electrode to the weld pool. In this method, oscillations areinduced in the pool by applying a force to the pool and then removingthe force so that the pool then continues to oscillate at substantiallyits natural frequency. The frequency of these oscillations is measuredafter the removal of the force, and compared with a parameterrepresenting a desired value of this frequency. Thereafter, theelectrical current passing through the arc is adjusted so that themeasured frequencies will approach the desired value of this frequency.(This method may hereinafter by referred to as the "weld pool masscontrol method" of the invention).

This invention also provides an apparatus for use in measuring thefrequency of oscillation of the weld pool in an arc welding process inwhich an electrical current forms an arc from an electrode to the weldpool. This apparatus comprises means for inducing oscillations in theweld pool including means for applying a force to and removing thisforce from the weld pool, so that the weld pool continues to oscillateat substantially its natural frequency following the removal of theforce, and means for measuring the frequency of oscillation of the poolafter the force has been removed. This apparatus also comprises meansfor adjusting the electrical current of the arc in response to thedifference between the measured frequency of oscillation and a desiredvalue of this frequency. (This apparatus may hereinafter be referred toas the "weld pool mass/frequency measuring apparatus" of the invention.)

This invention also provides a method of locating a weld line in which abeam of light is directed onto a welding electrode disposed adjacent theweld joint preparation. The beam is reflected from the electrode ontothe weld joint preparation so as to form on the weld joint preparationan illuminated area traversing the weld line and having an irregularitywhen the illuminated area crosses the weld line. Location of the weldline there only involves determining the location of this irregularity.(This method of the invention may hereinafter for convenience bereferred to as the "reflected beam method" of the invention.)

This invention also provides apparatus for detecting a weld linecomprising an electrode having an axis, a tip and a sidewall, at least aportion of the sidewall being capable of reflecting light. The apparatusalso includes a beam producing means for directing a beam of light ontothe reflective portion of the side wall, this beam being directed at anacute angle to the axis of the electrode and toward the tip of theelectrode so that the beam will be reflected from the sidewall and forman illuminated area on the surface of a workpiece lying adjacent the tipin a plane perpendicular to the axis. (This apparatus may hereinafter bereferred to as the "reflected beam apparatus" of the invention.)

This invention also provides a method for locating a weld line in whicha welding electrode is disposed adjacent a weld joint preparation and anelectrical arc is established between the electrode and the weld jointpreparation. The electrical arc is not sufficient to form a molten poolon the weld joint preparation, but is sufficient to generate light whichis reflected from the weld joint preparation. The light thus reflecteddisplays an irregularity at the weld line. Part of the reflected lightis received by a photodetector and the light thus received is analyzedto detect the irregularity, and thus the weld line. (This method mayhereinafter be referred to as the "low power arc method" of theinvention.)

This invention also provides apparatus for detecting a weld line, thisapparatus comprising a welding electrode and a power supply forsupplying electrical power to the electrode for maintaining an electricarc between the electrode and a weld joint preparation disposed adjacentthereto, this electrical arc not forming a molten pool on the weld jointpreparation but emitting light. The apparatus also comprises aphotodetector for receiving light emitted from the arc and reflectedfrom the weld joint preparation and an analyzer for analyzing the lightreceived by the photodetector and for detecting an irregularity in thelight indicative of a weld line on the weld joint preparation. (Thisapparatus may hereinafter be referred to as the "low power arcapparatus" of the invention.)

This invention also provides a method for locating a weld line in whicha pool of molten material is formed on a weld joint preparation, thispool traversing the weld line of the weld joint preparation. A leadingportion of the pool (i.e. a portion of the pool lying adjacent a part ofthe weld line over which the welding apparatus has still to pass) isallowed to flow between the two metal portions comprising the weld jointpreparation along the weld line, and this flow causes a concavedistortion in the surface of the leading portion of the pool where thisleading portion traverses the weld line. Light reflected from theleading portion of the pool is detected and analyzed to detect theconcave distortion and hence the weld line. (This method may hereinafterbe referred to as the "flowing pool method" of the invention.)

Finally, this invention provides apparatus for locating a weld lineincluding means for forming a pool of molten material on the weld jointpreparation, this pool traversing the weld line, a photodetector fordetecting light reflected from a leading portion of the pool and ananalyzer for analyzing the light detected by the photodetector so as todetect a concave distortion present in the leading portion of the poolwhere it crosses the weld line. (This apparatus may hereinafter bereferred to as the "flowing pool apparatus" of the invention.)

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevation of a first axial viewing apparatusof the invention;

FIG. 2 is a schematic side elevation of a second axial viewing apparatusof the invention;

FIG. 3 is a schematic side elevation of a third axial viewing apparatusof the invention;

FIG. 4 is a block diagram of the photodetector and analyzer apparatus(including a first video-computer interface) which can be used inconjunction with the optical viewing apparatus shown in any of FIGS. 1-3to carry out various methods of the invention;

FIG. 5 is a block diagram showing the main components of the firstvideo-computer interface shown in FIG. 4;

FIG. 6 is a wiring board connector strip diagram showing the connectionsbetween the various boards shown in FIG. 5;

FIG. 7 is a circuit diagram of the buffer board shown in FIG. 5;

FIG. 8 is a circuit diagram of the PIA/VIA SELECT, COMPUTERCOMMUNICATION block of the controller board shown in FIG. 5;

FIG. 9 is a circuit diagram of the row control portion of the controllerboard shown in in FIG. 5;

FIG. 10 is a circuit diagram of the column control portion of thecontroller board shown in FIG. 5;

FIGS. 11 and 12 are circuit diagrams of the memory board shown in FIG.5;

FIGS. 13A and 13B are circuit diagrams of the analog board shown in FIG.5;

FIGS. 14A and 14B are timing diagrams showing the temporal correlationbetween various signals generated in the circuits shown in FIGS. 5-13;

FIG. 15 is a flow chart showing the overall architecture of the computerprogram used in the computer shown in FIG. 4 to carry out the weldpuddle width measuring method of the invention;

FIG. 16A is a schematic plan view of a weld puddle the width of which isto be measured by the weld puddle width measuring method of theinvention;

FIG. 16B is a graph showing the light intensity distribution across adiameter of the weld puddle shown in FIG. 16A;

FIG. 17 is a flow chart of the program PWDTHX shown in FIG. 15;

FIG. 17A is a flow chart of the subroutine MEAN shown in FIG. 17;

FIG. 17B is a flow chart of the subroutine SLOPE shown in FIG. 17;

FIG. 17C is a flow chart of the subroutine SLP shown in FIG. 17B;

FIG. 17D is a flow chart of the subroutine EVALP shown in FIG. 17B;

FIG. 17E is a flow chart of the subroutine SMOOTH shown in in FIG. 17;

FIG. 17F is a flow chart of the subroutine SMTH shown in FIG. 17E;

FIG. 17G is a flow chart of the subroutine TRANSF shown in in FIG. 17;

FIG. 17H is a flow chart of the subroutine CLEAN shown in FIG. 17;

FIG. 18 is a block diagram of the welding process control apparatus usedfor controlling the width of the molten weld pool in the weld pool widthmeasuring method of the invention;

FIG. 19 is a block diagram of a weld pool mass/frequency measuringapparatus of the invention;

FIG. 20 is a block diagram showing in more detail the process controlcomputer, digital analog converter, analog output isolation amplifier,analog digital converter, and analog input isolation module shown inFIG. 19, together with various associated circuitry;

FIG. 21 is a circuit diagram showing in more detail the constant voltagepower supply, regulator module, control module and associated circuitryshown in FIG. 19;

FIG. 22 is a schematic circuit diagram of the power supply shown inFIGS. 20 and 21;

FIG. 23 is a schematic diagram of one of four identical heat sink unitsof the regular module shown in FIGS. 19-21;

FIG. 24 is a schematic circuit diagram of the analog input isolationunit shown in FIG. 19;

FIGS. 25A and 25B are schematic circuit diagrams of the analog outputisolation unit in FIG. 19;

FIG. 26 is a graph showing the temporal relationship between arc currentand arc voltage following arc pulsing in accordance with a weld pooloscillation method of the invention using the apparatus shown in FIGS.19-25;

FIG. 27 is a graph similar to FIG. 26 but showing the relationships asactually measured using a computer averaged arc voltage curve generatedin preferred weld pool oscillation method of the invention;

FIG. 28 is a flow chart showing the method used for continuous updatingand averaging of the arc voltage signal in the preferred weld pooloscillation method of the invention;

FIG. 29 is a flow chart showing the logic employed in the preferred weldpool mass measurement method of the invention;

FIG. 30 is a schematic elevation of the experimental "weld jointpreparation" shown in FIG. 19 and used for testing the weld poolmass/frequency measuring apparatus of the invention shown in FIGS.19-25;

FIG. 31 is a graph showing the temporal relationship between frequencyand base current in the absence of the weld pool mass measurement methodof the invention;

FIG. 32 is a graph similar to FIG. 31 but using the weld poolmass/frequency measurement method of the invention;

FIG. 33 is a flow chart of the computer program MAIN used in the weldpool mass/frequency measurement method of the invention;

FIG. 33A is a flow chart of the subroutine INIT shown in FIG. 33;

FIG. 33B is a flow chart of the subroutine USER shown in FIG. 33;

FIG. 33C is a flow chart of the subroutine INTHAN used to handleinterrupts in the program MAIN shown in FIG. 33;

FIG. 33D is a flow chart of the subroutines START and STOP called by thesubroutine PEND shown in FIG. 33J;

FIG. 33E is a flow chart of the subroutine PULSE shown in FIG. 33C;

FIG. 33F is a flow chart of the subroutine ATOD called by the subroutinePUSLSE shown in FIG. 33C;

FIG. 33H is a flow chart of the subroutine AVERG used in the subroutineCOMPUT shown in FIG. 33K;

FIG. 33I is a flow chart of the subroutine AVC called by the subroutinePULSE shown in FIG. 33E;

FIG. 33J is a flow chart of the subroutine PEND shown in FIG. 33C;

FIG. 33K is a flow chart of the subroutine COMPUT called by thesubroutine PULSE shown in FIG. 33E;

FIG. 33L is a flow chart of the subroutine JOG called by the subroutinePEND in FIG. 33J;

FIG. 34 is a flow chart showing the program used to carry out the logicshown in FIG. 29;

FIG. 35 is a schematic side elevation of a first reflected beamapparatus of the invention;

FIG. 36 is a plan view showing the illuminated area produced on a beveltype weld joint preparation using the reflected beam apparatus shown inFIG. 35;

FIG. 37 is a schematic side elevation of a second reflected beamapparatus of the invention;

FIG. 38 is a graph showing a line through the irregularity in theilluminated area shown in FIG. 36, together with the light intensityalong this line and the first and second derivatives of this intensity;

FIG. 39 is a flow chart of the main computer program used in the processcontrol computer shown in FIG. 4 to control the operation of thereflected beam apparatus shown in FIG. 35 or 37;

FIG. 40 is a flow chart of the subroutine TRACK shown in FIG. 39;

FIG. 41 is a flow chart of the subroutine LNGRES shown in FIG. 39;

FIG. 42 is a flow chart of the subroutine CONTROL shown in FIG. 39;

FIG. 43 is a schematic side elevation of a low-power arc apparatus ofthe invention;

FIG. 44A is a top plan view of a weld joint preparation in which theweld line is being followed by the flowing pool method of the invention;and

FIG. 44B is a section along the line 44B--44B in FIG. 44A.

FIGS. 45-51 are circuit diagrams of a second video-computer interfacewhich can be used in place of the video-computer interface shown inFIGS. 4-13B.

DETAILED DESCRIPTION OF THE INVENTION

From the Summary of the Invention above, it will be apparent that allthe methods and apparatus of the invention rely upon detection of lightfrom the weld joint preparation, and/or weld pool. The term "light" isused herein to mean electromagnetic radiation of a wavelength which canbe handled by optical devices such as lenses and cameras, and thusincludes not only the spectrum visible to the human eye but alsoportions of the infrared and ultraviolet regions. However, the term doesnot include electromagnetic radiation, such as gamma rays, which cannotbe handled by conventional optical devices. Terms such as"photodetector" used herein are to be construed accordingly.

The metal portions forming the weld joint preparation and lying oneither side of the weld line in the instant methods may be portions oftwo separate pieces of metal, or they may be two portions of the samepiece of metal which is desired to weld together. For example, the twometal portions might be opposite edges of a single sheet of metal whichhas to be welded together in order to form the sheet into a cylindricalor other prismatic housing. Also, in stating that two metal portions arepresent in the instant methods. I do not exclude the possibility thatthe two portions may already have been "tack" welded together in orderto hold them in the correct relative positions for further welding.

The term "non-directional weld line tracking system" is used herein todenote a weld line tracking system which can accommodate changes in thedirection of a weld line without requiring that a weld line sensor berotated around a welding torch. The term does not necessarily imply thatthe system can accommodate a 360° rotation of the weld line, but doesimply that substantial angular movement of the weld line from itsoriginal position can be accommodated without requiring theaforementioned rotation.

In all the methods and apparatus of the invention, when it is necessaryto detect light from the weld joint preparation and/or weld pool, it isadvantageous to view the weld joint preparation and weld pool, ifpossible, in a direction parallel to the axis of the welding electrodebeing used. (It should be noted that the reflected beam and low-powerarc methods of the invention are inherently restricted to electric arcwelding apparatus. However, the other methods of the invention are inprinciple applicable to any type of welding which involves a moltenpool, not necessarily electric arc welding, but are primarily intendedfor use in electric arc welding.) By using light traveling substantiallyparallel to, but spaced from, the axis of the electrode, an image of theweld joint preparation and weld pool can be obtained in which the verybright arc is hidden by the electrode, which makes it easier to analyzethe image seen.

AXIAL VIEWING SYSTEM Optical Apparatus

FIG. 1 is a schematic side elevation of a first axial viewing apparatus10, which has the form of a gas tungsten arc welding (GTAW) weldingtorch. The apparatus 10 comprises an electrode holder 11 which supportsa non-consumable tungsten electrode. This tungsten electrode has twosections at right angles to one another, namely a horizontal section 12adjacent the electrode holder 10 and a vertical section 13 which dependsvertically downwardly from the end of the horizontal section 12. FIG. 1shows the apparatus 10 in use; from the tip 14 at the lower end of thevertical section 13 of the electrode, an electric arc 15 extends to aweld joint preparation 16. This arc generates a molten weld pool 17which is viewed in a direction axially of the vertical section 13 of theelectrode by the axial viewing method of the invention, as describedbelow.

In order to permit inert gas purging of the weld torch so that argon oranother inert purge gas can be maintained around the weld pool 17 (thoseskilled in the art will be aware of the advantages of such inert gaspurging), a shielding gas retention tube 18 is provided surrounding thevertical section 13 of the electrode. The gas retention tube 18 hasthree sections, namely a narrow cylindrical section adjacent the tip 14of the electrode, a frusto-conical section above the narrow cylindricalsection, and an upper, wider cylindrical section which forms the mainpart of the gas retention tube 18. All three sections of the gasretention tube 18 are coaxial with the axis of the vertical section 13of the electrode. In order to accommodate the horizontal section 12 ofthe electrode and the electrode holder 11, the gas retention tube 18 isprovided with a side branch tube 19 coaxial with the axis of thehorizontal section 12 of the electrode. The interior of the branch tube19 communicates with the interior of the upper cylindrical section ofthe tube 18 via an aperture cut through the wall of this uppercylindrical section.

The upper end of the tube 18 is closed by a convex lens 20. The tube 18extends upwardly through a support member 21 so that the lens 20 liesabove the support member 21. A mirror 22 is mounted on the supportmember 21 by means of a mirror mount 23 so that the mirror 22 liesdirectly above the lens 20 and at an angle of 45° to the horizontal. Ata point on the support member 21 spaced from the lens 20, a secondconvex lens 24 is mounted on the support member 21 by means of a lensmount 25.

During welding, light from the weld pool 17 passes upwardly through thehollow interior of the tube 18 to form a beam 26. The beam 26 iscollimated by the lens 20 to form a vertical, parallel beam. Thisvertical beam is then reflected from the mirror 22 to form a horizontalbeam which is focused by the lens 24 so as to form an image of the weldpool (and, in practice, the surrounding area) in an image plane 27. Asthose skilled in the art are aware, during electric arc welding highintensity light is generated by the electric arc, which is confined tothe area between the tip of the electrode and the weld pool.Accordingly, in the apparatus shown in FIG. 1, the image produced in theimage plane 27 does not include an image of the electric arc itself,since the tip 14 of the electrode blocks direct light from the electricarc from entering the beam 26. Thus, by viewing the weld pool using thebeam 26, which comprises light traveling substantially parallel to, butspaced from, the axis of the vertical section 13 of the electrode, onecan obtain an image of the weld pool without seeing the very intensedirect light from the electric arc itself. The only light used to formthe image in the image plane 27 is light from the electric arc reflectedfrom the mirror-like surface of the weld pool, from the surroundingmetal which has not melted, and from the resolidified area immediatelybehind and adjacent to the path of the welding torch. The lightreflected from the unmelted metal and the resolidified weld metal ismore diffuse than the bright reflection from the mirror-like surface ofthe weld pool.

Those skilled in the field of optics will appreciate that if desired thelens 20 could be eliminated and an image of the weld pool andsurrounding areas formed solely by the lens 24. However, it is preferredthat the lens 20 be included to collimate the light in the beam 26,since such collimation produces an image in the plane 27 which is bothsharp and insensitive to the length of the optical path between the lens20 and the lens 24 i.e. with the lens 20 in position, the lens 24 can bemoved relative to the mirror 22 without altering the magnification ofthe image and without any need for refocusing. This ability to obtainconstant magnification regardless of the precise location of the lens 24is important since one of the uses made of this direct and undistortedview of the weld pool produced by the apparatus 10 is the measurement ofweld pool width.

In the apparatus 10, the lens 24 is preferably a telephoto lens focusedat infinity. Although the image produced in the image plane 27 can beviewed directly by eye (the use of safety glass to protect the eye fromultraviolet light present in the beam 26 is highly desirable), theapparatus 10 is primarily intended to be used with the image in theplane 27 being observed by a camera. This may be a film camera, but ispreferably a television camera, preferably a solid state televisioncamera.

The second axial viewing apparatus of the invention (generallydesignated 30) shown in FIG. 2 has a non-consumable electrode and may beused, for example, in gas metal arc welding (GMAW). The apparatus 30shown in FIG. 2 differs from the apparatus 10 shown in FIG. 1 in thatthe electrode holder 11 of the apparatus 30 has its axis vertical and inthat the electrode 13 of the apparatus 30 is linear, extendingvertically downwardly from the electrode holder 11 to the tip 14 of theelectrode. The electrode 13 is surrounding by a shielding gas retentiontube 31; because the electrode 13 is linear, this shielding gasretention tube, unlike the corresponding tube 18 shown in FIG. 1, needsno side branch. The tube 31 has substantially the same form as the tube18 shown in FIG. 1, having a lowermost narrow cylindrical sectionadjacent the tip 14 of the electrode 13, a frusto-conical centralsection and an upper, wider cylindrical section which accommodates theupper part of electrode 13 and the electrode holder 11. An aperture 32is formed in the wall of the upper cylindrical section of the tube 31and a mirror 33 is disposed within the tube 31 adjacent this aperture32, the mirror 33 being positioned at 45° to the horizontal. A centralaperture in the mirror 33 allows the electrode 13 to pass therethrough.The mirror 34 is mounted on the upper cylindrical portion of the tube 31by means of a mirror mount 35 so that the mirror 34 lies outside thetube 31 adjacent the aperture 32 and at 45° to the horizontal. A convexlens 35 is disposed in a horizontal plane above the mirror 34; themethod of mounting this lens 35 is not shown in FIG. 2, but obviously ifdesired the lens may be mounted by means of a suitable lens mountdirectly on the tube 31.

When the apparatus shown in FIG. 2 is in operation, it operates insubstantially the same manner as the apparatus shown in FIG. 1, with anelectric arc 15 extending from the tip 14 of the electrode 13 to a weldpool 17 disposed on the upper surface of a weld joint preparation 16lying beneath the electrode 13. As in the apparatus shown in FIG. 1,light reflected from the weld pool 17 and traveling substantiallyparallel to the axis of the electrode 13 passes upwardly along theinterior of the tube 31 as a beam 26. However, in the apparatus shown inFIG. 2, this beam 26 is deflected by the mirror 33 and passeshorizontally through the aperture 32. After passing through the aperture32, the beam strikes the mirror 34, which deflects it into a verticalpath so that it passes through the lens 35 and is brought to a focus inan image plane 36. For the reasons previously described with referenceto FIG. 1, the image formed in the image plane 36 does not include animage of the electric arc itself, since the arc is obscured by the tip14 of the electrode 13.

It should be noted that the apparatus 30 shown in FIG. 2 does notinclude any collimating lens equivalent to the lens 20 shown in FIG. 1and therefore it is important that the length of the optical path fromthe weld pool 17 to the image plane 36 be precisely controlled in orderthat the magnification of the optical system will be known. It isintended that the apparatus 30 shown in FIG. 2 be used with a televisioncamera or other camera or viewing device mounted on the tube 31 by meansof a camera mount 37 so as to receive the image produced in the imageplane 36. Obviously, a camera thus mounted directly upon the tube 31will follow all movements of the welding torch.

The third axial viewing apparatus of the invention, generally designated50 and shown in a highly schematic matter in FIG. 3, may be used, forexample, in a GMAW process and uses a consumable electrode in the formof a metal filler wire 51. As in the apparatus shown in FIGS. 1 and 2,an arc 15 is struck between the lower end of this wire 51 and produces aweld pool 17 on a weld joint preparation 16 disposed below the tip ofthe wire 51. Also, since the apparatus shown in FIG. 3 is again intendedto be used with an inert purge gas, the lower part of the wire 51 issurrounded by a gas retention tube 52. The gas retention tube has a formsimilar to the corresponding tube 31 shown in FIG. 2 except that itlacks the aperture in the side wall. Instead, the upper end of the tube52 is provided with a plexiglass cover 53 which has a small centralaperture to allow the passage of the wire 51 therethrough. This cover 53serves to limit leakage of inert purge gas from the top of the tube 52and also provides a transparent window at the upper end of the tube 52.A mirror 54 is disposed above the cover 53 at an angle of 45° to ahorizontal and a convex lens 55 is disclosed in a vertical plane somedistance from the lens 54.

As in the two axial viewing apparatus previously described, lightreflected from the weld pool 17 traveling substantially parallel to butspaced from the wire 51 passes upwardly along the tube 52 as a beam 26.This beam passes through the transparent cover 53 and the aperturetherein, and is reflected by the mirror 54 to form a horizontal beamwhich passes through the lens 55 and is thus focused to form an image inan image plane 56. As in the apparatus 30 shown in FIG. 2, the apparatusshown in FIG. 3 does not possess any collimating lens corresponding tothe lens 20 in FIG. 1 and thus the optical path from the weld pool 17 tothe image plane 56 must be held constant. Although for the reasonsalready explained, the absence of a collimating lens does havedisadvantages, the apparatus 50 is designed so that it is not necessaryto drill a hole through any lens. Those skilled in the art willappreciate that if desired the apparatus shown in FIGS. 1-3 could bemodified by including a lens within the gas retention tube 18, 31 or 52,this lens having an appropriate central aperture to allow the electrodeto pass therethrough. Use of such apertured lenses would avoid the useof mirrors to deflect the beam of light used to form the image out ofthe path of the electrode and thus the use of mirrors to avoid suchdrilling of apertures through lenses is simply a matter of choice. Also,when, as in the apparatus shown in FIGS. 2 and 3, no collimating lens ispresent, adjustment of magnification can be effected during initialset-up of the system and, provided all parts of the system remain in thesame relative locations, this magnification will not change.

As already mentioned, viewing the weld pool parallel to the axis of theelectrode in accordance with the axial viewing method of the inventionhas the advantage that the very bright electric arc is obscured by thetip of the electrode so that the weld pool can be viewed without beingobscured by this arc. In addition, this method enables the entire weldpool to be viewed without obstruction from any retaining apparatus usedto support the electrode. Any support structures for the electrode whichare located within the path of the light beam used to form the imagewill be located a substantial distance from the weld pool and will thusbe out of focus and not capable of blocking the view of the pool.Moreover, in the apparatus shown in FIGS. 1-3 the viewing lenses areprotected by the gas retention tube and by the purge gas itself fromdamage by the arc and any weld spattering that may occur, while theviewing system does not intrude into the vital space immediately aroundthe tip of the electrode and the weld pool and thus does not limitaccess to this area where space is limited.

It will be apparent to those skilled in the art that if desired theaxial viewing apparatus of the invention may be used with optical fibermethods to transmit the image to a remote location. Also, the axialviewing method of the invention may be used with welding processes thatdo not use any inert purge gas or gas retention tube.

FIG. 4 is a block diagram of the photodetector and analyzer apparatuswhich can be used in conjunction with any of the apparatus shown inFIGS. 1-3. The apparatus shown in FIG. 4 comprises a video (television)camera 68 which receives the image formed in the image plane 27, 36 or56 in FIG. 1, 2 or 3 respectively. Although the camera 68 may be of anyconvenient type, it is preferably a General Electric TN2500 videocamera. Modern solid state cameras, such as the General Electric TN2500,have a light sensitive surface formed from a matrix of discrete lightsensitive elements or pixels. The spatial resolution of such cameras isdetermined by the number and distribution of the pixels, which varieswidely from camera to camera; a camera having a 32×32 matrix will givevery coarse picture resolution, while the 244 vertical×248 horizontalarray used in the General Electric TN2500 is typical of the finerresolution of state of the art cameras. Although the TN2500 camera iscapable of operating in several different modes, the circuitry andsoftware described below are designed for use only with the camera inthe 30 Hz, 244 line sequential mode.

As is well known to those skilled in the art, video cameras generateanalog voltage signal representative of the image seen by the camera. Atthe beginning of each frame of this analog signal occurs a framesynchronization pulse normally referred to as the verticalsynchronization signal (VSYNC). Similarly, at the beginning of each linethe analog signal contains a synchronization pulse called the horizontalsynchronization signal (SBLNK). The analog signal from the video camerarepresents the image seen by scanning lines successively in a rasterpattern. The position of any line in this pattern may be determined fromthe time elapsed since the preceding vertical synchronization signal,while the horizontal position of any part of the signal can bedetermined from the time since the preceding horizontal synchronizationsignal.

The camera 68 transmits an analog signal representative of the imageseen to a video camera control unit 70. This unit 70 is of a type whichwill be familiar to those skilled in the art and contains ananalog/digital converter to generate digital signals representative ofthe analog signals, together with counters to generate line numbers fromthe synchronization pulses and digital signals representative of theposition in the image represented by each digital video signal. Thus,the unit 70 generates digitized video signals accompanied bycorresponding address locations related to the position on the screen ofthe pixel producing the corresponding digitized video signal. It shouldbe noted, that if a conventional videocon or orthocon type of camera isused as the camera 68, the spatial resolution of the digital signalproduced by the control unit 70 is determined by the rate at which thecontrol unit 70 digitizes the analog video signal from the camera 68,whereas with the discrete pixel type of cameras, such as the preferredGeneral Electric TN2500, the control unit 70 should be arranged so thata digital signal corresponding to each separate pixel of the camera isobtained. The control unit 70 sends digital and analog signals alongbuses 306 and 307 to a video-computer interface 100. This interface 100is connected to a process control computer 80 by a two-way bus 88. Theinterface is also connected via a video line 86 (actually a pair oflines are used, as discussed in more detail below with reference to FIG.5) to a double-trace oscilloscope 76, via a video line 82 to a videotape recorder 74 and via a video line 84 to a video monitor 72. Thevideo monitor allows an observer to observe the image seen by the camera68, while the video tape recorder 74 allows the image to be recorded forlater analysis.

The process control computer is in two-way communication, via a pair oflines 90, with a parallel communications interface which controls theoperation and positioning of the welding apparatus, and will bedescribed in more detail below.

One major problem in handling the digital video data from the controlunit 70 is the very high rate at which such data is generated. We havefound that for accurate analysis it is necessary to use an eight-bitgray tone scale. Using such an eight-bit scale with a 244×248 arrayrequires that over half a million data bits be handled for each frame ofpicture. The preferred TN2500 camera generates about 30 million databits (approximately 4 million bytes) per second. To analyze such astream of data continuously presents very great difficulties.Accordingly, to reduce the rate at which data must be analyzed, thevideo-computer interface 100 is arranged so that only certain parts ofcertain frames of the video signal from the control unit 70 are retainedfor analysis. For this purpose, the video-computer interface 100contains a buffer memory which can temporarily store video data from thecontrol unit 70 in order that such stored data can later be analyzed bythe computer 80, thereby enabling the computer to effect this analysisasynchronously of the signal from the control unit 70. In addition, thebuffer memory used only records the data from about 1/16 of the totalpixels in any selected frame, but the video-computer interface isprogrammable so as to allow an operator to select a specific "window" inthe image which is to be retained by the buffer memory, and also allowsskipping of rows and columns of pixels within this window.

It should be noted that, in contrast to some prior art systems, whichreduce the amount of data to be analyzed by converting the video signalto a binary image with white being assigned to brightness greater than athreshhold level and black being assigned to brightness lower than thethreshhold level, the apparatus shown in FIG. 4 does allow for thehandling of the video data on an eight-bit gray tone scale, thusallowing much more sophisticated analysis.

FIRST VIDEO-COMPUTER INTERFACE

FIG. 5 shows the main components of the video-computer interface 100shown in FIG. 4. The video-computer interface 100 comprises fourseparate boards, namely a buffer board 110, a controller board 140, ananalog board 280 and a memory board 274; these boards are indicated bythe broken boundaries in FIG. 5.

The buffer board 110 serves to interconnect the remaining three boardsand also handles communication with the computer 80 (FIG. 4). (Thepresence of the computer 80 is not strictly necessary since the variousinputs from this computer to the video-computer interface 100 could bemanually generated or input. However, the use of the computer not onlyenables automatic analysis of the video data to be achieved but alsoallows more convenient changes in the parts of the video data to beretained in the buffer memory.)

As shown in FIG. 5, the buffer board 110 comprises a COMPUTER SIGNALBUFFERS section 110A and a BLOCK SELECT INPUT/OUTPUT CONTROL section110C linked by an internal bus 110B. The section 110A is connected tothe computer 80 (FIG. 4) by a computer data bus 284, a computer addressbus 286 and a further bus 287 which carries various miscellaneoussignals between the buffer board and the computer 80. These three buses284, 26 and 287 together comprise bus 88 shown in FIG. 4. The section110A is linked to all the other three boards by a two-way bus 288 and isalso, as already mentioned, linked to the section 110C via the internalbus 110B. The section 110C generates a device select signal, DS on aline 291, and a memory inhibit signal, MI on a line 292, both thesesignals being sent from the section 110C to both the controller board140 and the memory board 274. The section 110C of the buffer board 110also generates various other signals used by the other boards, asexplained in more detail below, but these additional signals have beenomitted from FIG. 5 for the sake of clarity.

The controller board comprises a PIA/VIA SELECT COMPUTER COMMUNICATIONsection 140A, a column control section 140B and a row control section140C. All three sections of the controller board 140 are interconnectedby internal connections which will be discussed in more detail below.All three sections receive signals from the bus 288. The section 140Areceives an element rate clock signal ERC from the video camera via aline 307A, which is one of the lines in the bus 307 shown in FIG. 4.Section 140A inverts this signal to produce a corresponding invertedsignal ERC, which is then passed to the row control section 140C. Boththe section 140A and the row control section 140C receive the verticalsynchronization signal VSYNC from a line 307B, which is also part of thebus 307 shown in FIG. 4. Furthermore, both the section 140A and the rowcontrol section 140C receive the inverse horizontal synchronizationsignal SBLNK on a line 307C, a further line of the bus 307 shown in FIG.4. The section 140A generates, inter alia, a computer/camera controlsignal COM/CAM, which is placed on a line 304 in order to pass thissignal to the memory board 274.

The row control section 140C generates an End-Of-Frame signal, EOF,which is passed to the section 140A, and an "accept row" signal ACCROW,which is passed to the column control section 140B. The column controlsection 140B receives the signal ACCROW from the row control section140C and other signals (described in more detail below) from the section140A, and outputs, on a line 141, an "accept pixel" signal, ACCPIX,which indicates that the pixel from which video data is being receivedon the bus 306 from the camera 68 via the video camera control unit 70(FIG. 4) is one of the pixels selected by the operator for the retentionof video data. The ACCPIX signal on line 141 is sent to both the memoryboard 274 and the analog board 280.

The memory board 274 comprises a memory control section 274A linked to amemory-odd addresses section 274B hereinafter sometimes for convenienceabbreviated odd memory section 274B) and to a memory-even addressessection 274C via busses 276 and 278 respectively. The memory controlsection 274A receives digital video data from the bus 306, address andother data on the bus 288, the DS and MI signals from section 110C ofthe buffer board 110 via lines 291 and 292 respectively, the COM/CAMsignal on line 304 from the section 140A of the controller board 140,the ACCPIX signal on line 141 and signals ERC and VYSNC from lines 307Aand 307B. The memory control section 274A arranges for a pre-selectedportion of the digital video data arriving on the bus 306 to be storedin the memory sections 274B and 274C; the use of two memory sections isnecessary because the memories used are not sufficiently quick to storevideo data at the rate it is received on the bus 306 and thus the memoryboard 274 makes use of the special data handling techniques of theinvention.

Finally, the analog board 280 comprises a digital input/output section280A, a pair of digital-to-analog converters 280B and a summer section280C. The section 280A receives signals from the bus 288 and from thesection 140A. Its output comprises a signal IIG on a line 307D, whichforms part of the bus 307 (FIG. 4). The IIG signal is an inject inhibitsignal sent from the analog board to the camera 68 via the control unit70 (FIG. 4) which causes integration of the image intensity by thecamera over more than one frame, thereby producing a more intense image.Thus, the IIG signal is used to control the intensity of the image whichis transmitted from the camera to the video-computer interface.

The digital-to-analog converters 280B receive signals from the bus 288and from the section 140A and output, on the two lines 86 leading to theoscilloscope 76 (FIG. 4) analog signals representative of various datastored in the video-computer interface. The lines 86 carry signals tothe twin inputs of the oscilloscope 76, which is of the double-tracetype.

The summer section 280C of the analog board 280 receives an analog videosignal along line 307E, which is a further line of the bus 307 (FIG. 4).The summer section also receives the ACCPIX signal on line 141 from thecolumn control section 140B of the controller board 140 and outputs, viathe lines 84 and 82 to the monitor 72 and the video tape recorder 74respectively (FIG. 4), a highlighted video signal which indicates to theoperator the "window" currently being used i.e. the pixels of the imageseen by the camera 68 (FIG. 4) from which the video-computer interfaceis currently accepting video data.

Before the detailed circuitry of the video-computer interface shown inFIGS. 6-13B is described, it is convenient to summarize the signalswhich are generated by the video camera 68 (FIG. 4) and used by thevideo-computer interface 100. Further information concerning thesesignals and other matters relating to the camera 68 may be obtained fromthe manufacturer's literature relating to the General Electric TN2500camera.

The vertical synchronization VSYNC provides a pulse that denotes thestart of each frame of video data when the camera is operated in theinterlaced mode or each frame in the camera is operated in itssequential mode. The synchronized blanking logic or horizontalsynchronization signal, SBLNK indicates the start of each line of videodata. A high level of this signal indicates the presence of digitalvideo data, while a low level indicates the presence of a horizontal orvertical blanking signal, during which no digital video data ispresented. ERC is an element rate clock signal, of frequency 4.5045 MHz,which undergoes one complete cycle for each pixel of video datatransmitted by the camera.

The video computer interface shown in FIGS. 5-13B is designed to be usedwith the camera in the interlacing mode, in which each line of videodata is duplicated to enhance picture density. For obvious reasons, itis not desirable to store every line of video data within the windowsince half of the resultant video data would be redundant. Accordingly,as will be described in more detail below, the controller board 140 isarranged to divide the frequency of the horizontal blanking signal by 2,thereby producing a half-speed horizontal synchronization signalSBLNK/2, which is thereafter used to ensure that only one of eachidentical pair of lines within the preselected window is stored, theredundant lines simply being discarded.

The circuits of the video-computer interface 100 shown in FIGS. 6-13Bmake extensive use of large scale integrated circuits, some of whichcontain several separate circuits. In many cases, the individualcircuits on a single chip are used in widely separated parts of thecircuitry. Hereinafter for convenience, each integrated circuit will begiven a single number, and the separate circuits on the same chip willbe indicated by letters following the chip number. Thus, for example,128A and 128B represent separate circuits located on the same chip butused in two different parts of the circuitry. Also, in FIGS. 7-13B powerconnections to the various integrated circuits are omitted in most casessince details of the necessary power connections are readily availablein the standard literature.

FIGS. 6 and 7 show the detailed circuitry of the buffer board 110 (FIG.5) and the manner in which interconnections among the four boards areestablished. The easiest way to appreciate the interrelationship ofFIGS. 6 and 7 is to place the left-hand edge of FIG. 6 adjacent theright-hand edge of FIG. 7 to illustrate the numerous interconnectionsbetween the buffer board and the other three boards. Since several ofthe signals placed on the connectors shown in FIG. 6 are actuallygenerated by the circuitry shown in FIG. 7, the buffer board circuitryshown in FIG. 7 will be described before the interconnections shown inFIG. 6 are set out in detail.

The left-hand side of FIG. 7 shows the computer data bus 284, thecomputer address bus 286 and the third bus 287 which all connect thebuffer board to the computer 80 (FIG. 4). The letters and numerals onthe extreme left-hand side of FIG. 7 represent the lines of the AIM-65J3 connector which is used to establish all connections between thebuffer board and the computer. Further details concerning this connectormay be obtained from the manufacturer's literature concerning the AIM-65computer, and the nomenclature used for the various lines is thestandard nomenclature used in the manufacturer's manual.

The first part of the circuitry shown in FIG. 7 to be described will bethat used to generate the device select signal DS which has already beenreferred to above with reference to FIG. 5, and its inverse DS. As willbe explained in more detail below, the video-computer interface shown inFIGS. 5-13B contains 4K of memory, and this memory must be capable ofbeing address by the process control computer. The circuitry used togenerate the device select signal selects which 4K block of memoryaddresses from the computer will be alloted to the 4K memory in theinterface. Since each 4K block of memory within the computer is definedby the most significant digit of a four-digit hexadecimal number, onlyaddresses arriving on the computer address bus 286 and having thecorrect most significant hexadecimal digit should cause operation of thevideo-computer interface. Accordingly, the buffer board 110 is arrangedto generate the device select signal when the most significanthexadecimal digit arriving on the address bus has a preselected value.For convenience, this circuitry is arranged so that the most significanthexadecimal digit which will cause generation of the device signal canbe varied.

As shown in FIG. 7, lines 15-12 of address bus 286, which carry the mostsignificant hexadecimal digit of the four-digit hexadecimal number onthe address bus 286, are connected to pins 20-23 respectively of anintegrated circuit 116, which is a Schottky 4-line to 16-linedecoder/demultiplexer of the commercially-available 74LS154 type. Pins18 and 19 of circuit 116 are grounded, thus permanently enabling thiscircuit for decoding. As is well known to those skilled in the art, the74LS154 integrated circuit functions so that when pins 18 and 19 areheld low, receipt of a 4-bit number at pins 20-23 will cause one of the16 outputs (pins 1-11 and 13-17) to go low, the output which goes lowbeing determined by all four incoming bits. In the instant buffer board,only output pins 6-11, 13 and 14 of circuit 116 are used, and theseoutput pins are connected to pins 8-1 respectively of an integratedcircuit switching assembly 118, which comprises eight parallel singlepoles single throw DIP switches. The output pins 9-16 of switch assembly118 (which correspond to the inputs at pins 8-1 respectively) arejumpered and the jumpered output, which comprises the inverse deviceselect signal DS, fed to the line 291. The jumpered output from pins9-16 of 118 is also fed to pin 3 of 120A. Integrated circuit 120 is ahex inverter of the commercially-available 74LS04 type. The invertedoutput from pin 4 of circuit 120A is the device select signal DS, whichis placed on the line 290. (As will be explained below, integratedcircuit 120 is physically present on the controller board and part 120Athereof is only shown in FIG. 7 for the sake of ease of explanation. Infact, the DS signal from circuit 118 is taken to connector C9 on thecontroller board as explained below, and fed thence to pin 3 of inverter120A on the controller board. The inverted output from pin 4 of 120A isfed back to the buffer board via connector CF of the controller board.)

As will be apparent to those skilled in the art, switching assembly 118is set so that one of the switches is closed and the remaining seven areopen. Thus, the jumpered output will be high except when the inputconnected to the closed switch goes low, which occurs when lines A12-A15are carrying a preselected hexadecimal digit; since only outputs 6-11,13 and 14 of 116 are used, this predetermined hexadecimal digit canrange from 5 to C. Normally, assembly 118 is set with the switchconnecting pins 4 and 13 closed, which sets the preselected hexadecimaldigit to 9.

The remaining 12 lines of the computer address bus 286 are handled bytwo bi-directional buffers 122 and 126, which are each a hex, 3-statebuffer of the commercially-available 74LS367 type. Lines 11-6 ofcomputer address bus 286 are fed to pins 14, 2, 12, 4, 10 and 6respectively of buffer 122, while lines 5-0 of bus 286 are fed to pins14, 2, 12, 4, 10 and 6 respectively of buffer 126. Pins 1 and 15 of bothbuffers 122 and 126 are grounded, thus permanently enabling the buffersfor transmission of data from the bus 286 to the outputs of the buffers.The outputs at pins 13, 3, 11, 5, 9 and 7 of buffer 122 (whichcorrespond to the inputs of pins 14, 2, 12, 4, 10 and 6 respectively andthus to the signals on lines 11-6 of bus 286) are placed on lines 19-14respectively of bus 288. Similarly, the output to pins 13, 3, 11, 5, 9and 7 respectively of buffer 126 (which correspond to the signals onlines 5-0 of bus 286) are placed on lines 13- 8 respectively of bus 288.

As already mentioned above with reference to FIG. 5, the buffer boardgenerates a memory inhibit signal, which is used to inhibit writing tothe memory when this is necessary. Also as already explained, thevideo-computer interface contains 4K (4096) addresses, and any one ofthese addressed can be selected by the appropriate signals on lines 11-0of computer address bus 286. Sixty-four of these addresses do notaddress memory directly; instead, these 64 addresses (combinations ofsignals on lines 11-0 of bus 286) are used to control the operation ofthe interface. Thus, the memory inhibit signal is generated to inhibitwriting of data into the memories (to be described below) when theaddress designated on lines 11-0 of the address bus 286 is one whichdoes not require writing into memory.

To generate the memory inhibit signal, MI, the outputs from pins 13, 3,11, 5, 9 and 7 of buffer 122 (which correspond to the signals on lines11-5 of the address bus 286) are fed to pins 1-6 respectively ofintegrated circuit 124, which is an 8-input NAND gate of thecommercially-available 74LS30 type. The remaining two inputs, pins 11and 12, of gate 124 are held high, being connected to the +5 V supplyline. The output at pin 8 of gate 124 is the memory inhibit signal, MI,and is placed on the aforementioned line 292.

It will be apparent to those skilled in the art that MI will only go lowwhen the signals on lines 11-6 of bus 286 are all high i.e. when thehexadecimal address on bus 286 is from YFCO-YFFF where Y is anyhexadecimal digit, since integrated circuits 122 and 124 are enabledregardless of the most significant hexadecimal digit (i.e. regardless ofthe value of DS). Accordingly, selection of the actual 64 reservedaddresses is achieved using combinations of MI and DS (or DS), asdescribed in detail below. Note also that these 64 reserved addressesare the highest 64 addresses beginning with the preselected digit i.e.they are the highest 64 addresses in the 4K block assigned to thevideo-computer interface. As explained below, when the interfaceacquires video data, this data is stored sequentially in the addressesof the interface in ascending order. Thus, by reserving the highest 64address one ensures that the sequence of stored video data is notinterrupted by the block of reserved addresses, since such interruptioncould lead to difficulties in reading and analysis of the video data.

As shown in the bottom left-hand part of FIG. 7, bus 287 comprises linesW, Y, V, 4, 6, 7 and 22 of the aforementioned J3 connector. Line 4carries an interrupt signal, IRQ, line 6 carries signal NMI from thecomputer, line 7 carries a reset signal, RESET, and line 22 carries aground; these four lines simply pass straight through the buffer boardand are placed on lines 22-25 respectively of bus 288.

The remaining signals carried by bus 287 are a read/write signal R/W online V, the inverse of this read/write signal on line W and a computerclock signal φ2 on line Y. The signal R/W is fed to pin 14 of anintegrated circuit 130A. Integrated circuit 130 is a three-state hexbuffer of the commercially-available 74LS367 type provided with theconventional power connections at pins 16 and 8 (not shown) and withpins 1 and 15 connected to the +5 V supply line (as shown on inverter130B of the integrated circuit described below) so that the six driversof the integrated circuit are permanently enabled. The output from pin13 of 130A is placed on line 21 of bus 288. Similarly, the φ2 clocksignal is fed to pin 4 of 130B, a further driver of the integratedcircuit 130 just mentioned. The corresponding output from pin 5 of 130Bis placed on line 20 of bus 288. Hereinafter, when a reference is madeto the signals R/W and φ2, it should be understood that these are thesignals which have passed through the drivers 130A and 130Brespectively.

In addition to being placed on lines 20 and 21 of the bus 288, thesignals R/W and φ2 are also subjected to a gating process in order tocontrol enabling of a pair of buffers (described below) which controlthe two-way transmission of data between the computer data bus 284 andother parts of the video computer interface. The read/write signal R/Wand its inverse are signals which indicate the direction in which datatransmission should take place between the computer data bus 284 andlines 0-7 of bus 288. To produce appropriate enabling signals, the φ2signal from pin 5 of 130B is fed to pin 4 of a NAND gate 128A. Gate 128Acomprises part of an integrated circuit 128, which is a triple 3-inputNAND gate of the commercially-available 74LS10 type. The second input togate 128A at pin 3 thereof is the inverse read/write signal, while thethird input to gate 128A at pin 5 is the DS signal from pin 4 ofinverter 120A. The output from pin 6 of gate 128A is supplied to pin 1of each of a pair of buffers 112 and 114.

In addition to being supplied to pin 4 of 128A, the φ2 signal from pin 5of 130B is supplied to pin 11 of 128B, a second NAND gate on the sameintegrated circuit 128. The second input to pin 9 of 128B is the R/Wsignal from pin 13 of driver 130A, while the third input to pin 10 of120B is again the DS signal from pin 4 of inverter 120A. The output frompin 8 of 120B is fed to pin 1 of 128C, the third NAND gate on the sameintegrated circuit 128. The remaining two inputs to pin 128C, pins 2 and13, are held high, being connected to a +5 V supply line, so that gate128C acts an inverter. The output from pin 12 of 128C is supplied to pin15 of each of the aforementioned buffers 112 and 114.

It will be apparent to those skilled in the art that the outputs fromgate 128A and 128B will not go low unless the signal DS goes high i.e.unless the hexadecimal digit on line 15-12 of computer address bus 286has the correct value, thus indicating that the address on lines 11-0 ofthe same bus is one to which the video-computer interface shouldrespond. Also, the outputs from gate 128A and 128B cannot go low unlessthe clock signal φ2 goes high, a condition which indicates that thecomputer is ready to receive or transmit data. When both theseconditions are fulfilled, if the inverse read/write signal fed to pin 3of gate 128A is high (i.e. the read/write signal R/W is low), the outputat pin 6 of gate 128A will go low. On the other hand, if the read/writesignal R/W itself is high, the output at pin 8 of gate 128B will go lowand the output of pin 12 of gate 128C will go high.

The aforementioned buffers 112 and 114 are bi-directional buffers of thecommercially-available 8T26A type, manufactured by SigneticsCorporation. As already mentioned, pin 1 of each of these buffersreceives the output from pin 6 of gate 128A, while pin 15 of each bufferreceives the output from pin 12 of gate 128C. Pins 10, 6, 13 and 3 ofbuffer 112 are connected to lines 7-4 respectively of the computer databus 284. Similarly, lines 10, 6, 13 and 3 of buffer 114 receive lines3-0 respectively of computer data bus 284. Pins 9 and 11 of buffer 112are connected to line 7 of bus 288. Similarly, pins 5 and 7 of buffer112 are connected to line 6, pins 12 and 14 of buffer 112 to line 5 andpins 2 and 4 of buffer 112 to line 4 of the same bus. In an exactlysimilar manner, pins 9 and 11 of buffer 114 are connected to line 3 ofbus 288, pins 5 and 7 of buffer 114 to line 2, pins 12 and 14 of buffer114 to line 1 and pins 2 and 4 of buffer 114 to line 0 of the same bus.Thus, buffers 112 and 114 establish two-way communication between lines7-0 of the computer data bus 284 and lines 7-0 of bus 288, the directionof transmission being governed by the sign of the read/write signal R/W;when R/W is low, the direction of transmission will be from bus 284 tobus 288, while when R/W goes high, the direction of transmission will bein the opposed direction.

To sum up, the circuitry shown in FIG. 7 produces a low value of theinverse device select signal DS on line 291 when the most significanthexadecimal digit of the address arriving on the computer address bus286 has a preselected value indicating that the address is one whichrequires action by the video-computer interface. Under these sameconditions, the DS signal on line 290 goes high. When the aforementionedhexadecimal digit has the preselected value and the signals on lines11-0 of computer address bus 286 indicate that the address beingreceived is one of the 64 addresses which controls operation of theinterface rather than writing into memory, the memory inhibit signal MIis placed on line 292. Buffers 122 and 126 provide buffered transmissionfrom lines 11-0 of computer address bus 286 and lines 19-8 of bus 288.Buffers 112 and 114 provide two-way transmission between lines 7-0 ofthe computer data bus 284 and lines 7-0 of bus 288, the direction oftransmission depending upon the sign of the read/write signal R/W. Lines20-25 of bus 288 receive the signals from, or transmit the signals to,bus 287, except that the inverse read/write signal on line W of bus 287is not placed on bus 288.

The interconnections between the four boards shown in FIG. 6 will now bedescribed, together with the auxiliary circuitry shown in FIGS. 6. Asshown in that figure, each of the three boards 140, 274 and 280 isprovided with connectors 1-22 and A-F, H, J-N, P and R-Z. Forconvenience, the connectors on the controller board 140 may hereinafterbe referred to by a number or letter prefixed by "C", while theconnectors on the memory board 274 and the analog board 280 maysimilarly be referred to with prefixes "M" and "A" respectively. Each ofthe three boards 140, 274 and 280 fits into the buffer board 110 so asto lie perpendicular to the plane thereof and contacts between the fourboards are established by means of edge connectors on the controller,memory and analog boards and a bus on the buffer.

As shown in FIG. 6, lines 7-0 of bus 288 (which handle two-waycommunication with the computer data bus 284, as described above) areconnected to connectors 1-8 respectively on each of the three boards140, 274 and 148. Line 291, carrying the signal DS, is connected toconnector 9 on each board, while line 290, carrying the DS signal isconnected to connectors CF, AF and MU. Line 292, carrying the signal MI,is connected to connector 10 on each of the boards 140, 274 and 280.Lines 19-8 of bus 288 (which, as explained above, carry the twelve leastsignificant bits from lines 11-0 respectively of computer address bus286) are connected to connectors 11-22 respectively on each of theboards 140, 274 and 280.

Lines 20-24 of bus 288 (carrying signals φ2, R/W, IRQ, NMI, and RESETrespectively) are connected to connectors V, W, X, Y and 2 respectivelyof each of the boards 140, 274, and 280. Line 25 of bus 288, the groundline, is connected to a conventional ground circuit (only the connectorthereto shown in FIG. 6, since an appropriate form of ground connectionwill, it is believed, be readily apparent to those skilled in the art),and the same ground is connected to connector A on each of the boards140, 274 and 280. Connector B on each of the same three boards receives+5 V from a conventional stabilized power supply (again not shown sinceit will be apparent to those skilled in the art). Connectors CC and ACare interconnected by a line which carries a control signal CSB,connectors CD and AD are interconnected by a line which carries a signalCSA and connectors CE and AE are interconnected by a line which carriesa control signal CSF; all these three control signals are generated onthe controller board 140 in a manner to be described below. ConnectorsAH and AJ receive +12 V and -12 V respectively from a conventionalstabilized power supply (which will not be described in detail since itis believed that appropriate power supply circuit will be obvious tothose skilled in the art.) Connectors AK and AL are video outputconnectors which supply the analog outputs on lines 86 to theoscilloscope 76 (FIG. 4).

Connectors C-F, H and J-L on the memory board 270 receive lines 7-0respectively of the computer data bus 306. (For convenience, hereinafteran abbreviated form may be used to indicate lines in busses; for example306-7 indicates line 7 of bus 306 and similarly for other lines andbusses.) The vertical synchronization signal VSYNC received from thecamera on line 307B is passed to circuit 130C, a third driver on the74LS367 integrated circuit 130B previously described. The correspondingoutput at pin 3 of 130C is passed to connector CK. Similarly, thehorizontal synchronization signal SBLNK received from the camer on line307C is passed to pin 10 of 130D, a further driver of the 74LS367integrated circuit 130, and the corresponding output from pin 9 of 130Dis passed to connector CL. (All the integrated circuits shown on theright-hand side of FIG. 6 are physically located on the buffer board110.) The ERC signal received from the camera on line 307A in fed to pin12 of 130E, a further driver on integrated circuit 130, and thecorresponding output from pin 11 of 130E is fed to connector M on eachof the boards 140, 274 and 280.

Connectors CN and MN are interconnected by a line which carries theaccept pixel signal, ACCPIX generated on the controller board in amanner described below. Connector AN is connected to pin 6 of 130F, thesixth and final driver on the integrated circuit 130 previouslymentioned. The corresponding output at pin 7 of 130F is the IIG signalwhich is fed to the camera on line 307D, as described above withreference to FIG. 5. Connectors CP and MP are interconnected by a linewhich carries a "clear" signal CLR generated on the controller board 140in the manner described below. Also, connectors CR and MR areinterconnected by a line which carries the COM/CAM signal generated onthe controller board as described below; this interconnection betweenconnectors CR and MR is the line 304 shown in FIG. 5. Connectors CT andAP are interconnected by a line which carries a half-speed horizontalsynchronization signal SBLNK/2 generated on the controller board 140 asdescribed below.

Connector AR is the video output from the analog board and is connectedto line 84 as described above with reference to FIG. 5. Thecorresponding video input to the analog board on line 307E is taken toconnector AT. Both lines 84 and 307E are conventional coaxial videolines, grounding for which is provided from connector AS, which is alsoconnected to line 25 (the ground line) of bus 288.

Connectors CU and AU are interconnected by a line which carries theaccept pixel signal, ACCPIX, generated on the controller board 140.

Finally, as shown in the lower right-hand corner of FIG. 6, the G1, G2,I/244, N/122 and AGC signals from the TN2500 camera, are fed to a DIPswitch 111. This switch 111 grounds all of these signals except theN/122 signal, thereby holding the camera in the proper 30 Hz. sequentialmode.

FIG. 8 shows the section 140A of the controller board (see FIG. 5). InFIGS. 8-13B, references beginning with C, M or A appearing at theextreme left or right-hand edges of the figure indicate the connectorsshown in FIG. 6 which carry the corresponding signals.

The circuitry shown in the lower part of FIG. 8 is responsible forhandling and modifying various signals from the video camera to producesignals for use by other parts of the video-computer interface. Thevertical synchronization signal VSYNC, received via connector CK, is fedto pin 5 of 120B, a second inverter on the 74LS04 integrated circuit 120already mentioned. The corresponding inverted output from pin 6 of 120Bis the inverse vertical synchronization signal VSYNC, also designatedCLR, which is passed to the memory board via connector CP as describedabove. The CLR signal is also used in the row control portion 140C ofthe controller board, as described below with reference to FIG. 10. TheERC signal received from the video camera via connector CN is passed topin 13 of 120C, a further inverter on the 74LS04 integrated circuitalready mentioned, and the corresponding output at pin 12 of 120C is thesignal ERC, which is used in the column control section 140B of thecontroller board, as described below with reference to FIG. 10.

The horizontal synchronization signal SBLNK, received from the cameravia connector CL, is fed to pin 12 of integrated circuit 148, which is adual J-K positive-edge-triggered flip-flop of the commercially available74LS109 type. Although this integrated circuit contains two separateflip-flops, only the second flip-flop is used. Accordingly, pins 1-5 ofcircuit 148 are connected to the +5 V supply line and no connections aremade to the outputs from pins 6 and 7. Pins 11 and 14 (the 2PR and 2Jinputs respectively) of circuit 148 are connected to the +5 V supplyline, pin 13 (the 2K input) is grounded, and pin 15 (the clear input forthe second flip-flop) receives the signal VSYNC from pin 6 of inverter120B.

Integrated circuit 148 acts as a frequency-divider. As explained above,the video-computer interface shown in FIGS. 5-13B is designed for usewith the preferred General Electric TN2500 video camera in theinterlacing mode, in which each line of video data is repeated twice.The horizontal synchronization signal SBLNK undergoes one cycle for eachline of video data whether that line represents new data or merely arepetition of the previous line. In order to ensure that the videocomputer interface does not store random data, it is necessary to dividethe frequency of the horizontal synchronization signal by 2, therebyproducing a signal which only undergoes a single cycle for each new lineof video data. This frequency division by 2 is accomplished by theflip-flop on integrated circuit 148. This flip-flop is reset by thesignal VSYNC at the beginning of at the beginning of video data andthereafter operates using the horizontal synchronization signal SBLNK asits clock signal. Thus, the Q and Q outputs from pins 10 and 9respectively of circuit 148 are a half-speed horizontal synchronizationsignal SBLNK/2 and its inverse respectively. The SBLNK/2 from pin 10 of148 is fed to connector CT (for passage to the analog board 280, asdescribed above with reference to FIG. 6) and is also fed to integratedcircuit 162 pin 14 and integrated circuit 167A, pin 12, as describedbelow with reference to FIG. 9. The inverse signal from pin 9 of 148 isfed to integrated circuit 154, pin 14, flip-flop 166A, pin 1 andflip-flop 166B pin 13, all described below with reference to FIG. 9.

The circuitry shown in FIG. 8 also includes an integrated circuit 144,which is a dual 1-of-4 decoder/demultiplexer of thecommercially-available 74LS139 type. Integrated circuit 144 is used togenerate various control signals for controlling the operation of theR6520 and R6522 interfaces described below, circuit 144 varying thevalues of the various control signals in accordance with addressesappearing on the computer address bus 286 (FIG. 7) as transmitted to thecontroller board 140 via the bus 288 as already described.

The first part of integrated circuit 144, designated 144A in FIG. 8,receives at its pin 1 (its enable input) the memory inhibit signal, MI,received from gate 124 (FIG. 7) pin 8 via line 292 and connector C10.Pins 2 and 3 (the two select inputs) on 144A receive the signals onlines 13 and 12 respectively of bus 288 via connector C17 and C18respectively. As explained above with reference to FIG. 7, these signalson 288-13 and 288-12 correspond to the signals on lines 5 and 4respectively of the computer address bus 286. As may be seen from thetruth table for the 74LS139, when the memory inhibit signal goes low(thus indicating that the address appearing on the bus 286 is one of the64 addresses reserved for controlling the operation of thevideo-computer interface, rather than writing into the memory thereof),the input at one of outputs 4-7 of 144A will go low depending upon thetwo bits received at pins 2 and 3. Thus, each of the outputs 4-7 of 144Aproduces a low control signal only when one of 16 specific addressesappears on the computer address bus.

Pin 7 of 144A is not used. The output from pin 6 of 144A is fed to pin 1of 120D, which is a further inverter on the 74LS04 integrated circuit120 already described. The inverted output from pin 2 of 120B is acontrol signal hereinafter designated CSA, which is fed to connector CD(for transmission to the analog board 280, as described above withreference to FIG. 6), to integrated circuit 150 pin (described belowwith reference to FIG. 9) and to integrated circuit 160 pin (describedbelow with reference to FIG. 10). The output from pin 5 of 144A is acontrol signal hereinafter designated CSB, which is fed to connector CCfor passage to the analog board 280, as described above with referenceto FIG. 6. Finally, the output from pin 4 of 144A is a control signalCSC, which is fed to pin 23 of an integrated circuit 142 which isdescribed below.

The remaining half of integrated circuit 144, designated 144B in FIG. 8,has its pin 15 (enable input) grounded, so that 144B is permanentlyenabled. Pins 14 and 13 of 144B receive the signals from lines 11 and 10respectively of bus 288; as described above with reference to FIG. 7,these signals on lines 11 and 10 respectively of bus 288 correspond tothe signals on lines 3 and 2 respectively of computer address bus 286.

It will be apparent from the truth tables for the 74LS139, that, because144B is permanently enabled, one of its outputs at pins 9-12 will be lowdepending upon the value of the two bits received at its pins 13 and 14.Note that, unlike 144A, circuit 144B is not dependent for enablementupon MI and will thus produce its output depending upon the values ofthe bits on lines 3 and 2 of computer address bus 286, regards as theother 14 bits on bus 286. Pin 11 of 144B is not used. The output frompin 12 of 144B is a control signal CSD, which is fed to theaforementioned integrated circuit 150 (FIG. 9), pin 23. The output frompin 10 of 144B is a control signal CSE, which is fed to theaforementioned integrated circuit 160 (FIG. 10) pin 23. Finally, theoutput from pin 9 of 144B is a control signal designated CSF, which ispassed to connector CE for transmission to the analog board 280, asdescribed above with reference to FIG. 6.

The remaining integrated circuits are shown in FIG. 8 is a section 142Aof an integrated circuit 142 which is a Versatile Interface Adapter,namely a R6522 input/output port manufactured by Rockwell InternationalCorporation. Further details of this device may be obtained by referenceto Document No. 2900D47 Revision 1, published in Oct. 1978 by RockwellInternational Corporation. (Note that integrated circuit 142 is not acollocation of integrated circuits but a single unitary device; in thisparticular instance, the nomenclature 142A, 142B etc. is used solely forease of reference to the drawings since various parts of the integratedcircuit 142 are shown in FIGS. 8, 9 and 10, and the nomenclature doesnot imply that the various parts of integrated circuit 142 are in factacting independently.) Integrated circuit 142 serves as a multiple latchto store various parameters sent from the computer and required by thevideo-computer interface, and also handles various communications withthe video camera and the computer.

Pins 26-33 of 142A are connected to lines 7-0 respectively of bus 288;as explained above with reference to FIG. 7, these lines 7-0 of bus 288are in two-way communication via the buffers 112 and 114 with lines 7-0of the computer data bus 284. Pin 34 of 142A (the reset input) receivesthe RESET from line 287-7 via line 288-24 and connector CZ. Pins 35-38of 142A are connected to bus 288 lines 11-8 respectively via connectorsC19 and C22 respectively and thus receive signals corresponding to thefour least significant bits on the computer address bus 286, asdescribed above with reference to FIG. 7. Pin 25 of 142A receives the φ2signal from driver 130B (FIG. 7) via line 288-20 and connector CV. Pin22 of 142A receives the read/write signal R/W from pin 13 of driver 130A(FIG. 7) via line 288-21 and connector CW. Pin 24 of 142A receives thesignal DS from inverter 120A (FIG. 7) pin 4 via line 290 and connectorCF. (The effect of the connections to pins 23 and 24 of circuit 142A isthat 142A responds only to addresses XFCO-XFCF (where X is thepreselected hexadecimal digit which causes DS to go high) appearing onthe computer address bus 286 (FIG. 7). Pins 16 and 19 of 142A receivethe vertical synchronization signal VYSNC from pin 3 of driver 130C(FIG. 6) via connector CK. Pins 17 and 18 of 142A receive theend-of-frame signal EOF from gate 164A pin 13 (see description of FIG. 9below), pin 21 of 142A produces the interrupt signal IRQ, which isplaced on line 288-23 and passed via connector CX and line 287-4 (FIG.7) to the computer. This interrupt signal is generated by 142A whenevereither a VSYNC or a EOF signal is received by 142A and, as describedbelow, forces the computer to follow an interrupt routine. Pin 10 of142A produces the COM/CAM signal which is placed on line 304 and fed toconnector CR for transmittal to the memory board 274 as described abovewith reference to FIG. 6. The value of the COM/CAM signal is set by thecircuit 142A in accordance with instructions received from the computer;when this signal is set low, the memory board is instructed to acquirevideo data from the camera, while when COM/CAM is high the computer canread video data from the interface.

FIG. 9 shows the row control portion 140C of the controller board 140.This row control portion 140C counts the rows of video data, generatesappropriate signals when the video data being received from the camerais within the window previously set by the operator by defining firstand last rows of this window, and also gates the signals thus generatedby the row skip function previously set by the operator to determine forwhich rows within the window the video data are to be retained in thevideo-computer interface. The final output of the row control portion140C is the accept row signal, ACCROW, which indicates that the videodata being received from the camera relate to rows passing through thewindow and also that these rows are the selected rows within the window,as previously defined by the operator. Signal ACCROW is passed to thecolumn control portion 140B of the controller board 140, as previouslydescribed with reference to FIG. 5. The row control portion 140C is alsoresponsible for generating the end-of-frame signal, EOF, which is one ofthe signals used for generating the interrupt signal, IRQ, as previouslydescribed with reference to integrated circuit 142A in FIG. 8.

Storage of the numbers representing the first and last rows of thewindow is effected by an integrated circuit 150, which is a PeripheralInterface Adapter or input-output port of type R6520 manufactured byRockwell International. Further details of this integrated circuit maybe obtained from Document No. 29000D40, Revision 2, published in Oct.1978 by Rockwell International Corporation. Basically, as used in therow control portion 140C, this device acts as a multiple latch to storethe first and last row values.

Pins 26-33 of 150 receive signals from bus 288, lines 7-0 respectivelyvia connectors C1-C8 respectively. As explained above with reference toFIG. 7, the signals on bus 288 lines 7-0 are those from computer databus 284 lines 7-0 respectively, buffered by the buffers 112 and 114. Pin34 of 150 receives the RESET signal from line 287-7 via line 288-24 andconnector CZ. Pins 35 and 36 of circuit 150 receive the signals fromlines 9 and 8 respectively of bus 288 via connectors C21 and C22respectively; as explained above with reference to FIG. 7, these signalson lines 288-9 and 288-8 correspond to the 2 least significant bits ofthe address on the computer address bus 286. Pin 21 of circuit 150receives the signal R/W on line 288-21 from driver 130A pin 13 (FIG. 7)via connector CW. Pins 22 and 24 of circuit 150 receives device selectsignal DS from invertor 120A pin 4 (FIG. 7), while pin 23 of circuit 150receives control signal CSD from circuit 144B, pin 12 (see FIG. 8). Pin24 of circuit 150 receives control signal CSA from pin 2 of invertor120D (FIG. 8). As may be seen from consideration of the inputs to itspins 22-24, and the inputs to circuits 144A and 144B (FIG. 8), circuit150 is addressed by addresses XFDO-XFD3 appearing on the computeraddress bus 286 (FIG. 7).

Pin 25 of circuit 150 (the enable input) receives the φ2 signal fromdriver 130B pin 5 (FIG. 7) via line 288-20 and connector CV. Pins 18,19, 39 and 40 of circuit 150 are held high, being connected to the +5 Vsupply line via a resistor R1.

The effect of the connections to pins 21-36 on circuit 150 is that uponreceipt of a first appropriate address, XFDO, on the computer addressbus 286 (FIG. 7), the 8-bit value simultaneously appearing on thecomputer data bus 284 (FIG. 7) and representing the first row value willbe passed via bus 288, line 7-0 and latched in a first register incircuit 150. Similarly, upon receipt of a second address, XFD2 on thecomputer address bus 286 the 8-bit simultaneously appearing on computerdata bus 284 and representing the last row value will be latched into asecond register in circuit 150. The RESET input at pin 34 allows forresetting of circuit 150 when the computer, under the control of theoperator, indicates that such resetting is desired.

The first row value latched in circuit 150 appears at pins 2-9 (port Ain the manufacturer's nomenclature), while the last row value latched incircuit 150 similarly appears at pins 10-17 (port B in themanufacturer's nomenclature). These pins 2-17 of 150 provide the inputsto four integrated circuits 156, 157, 158, 159, each of which is a 4-bitmagnitude comparator of the commercially-available 74LS85 type. To avoidconfusion, input pin numbers are shown only on circuit 156, but thespatial arrangement of the inputs to each of the remaining threeintegrated circuits 157, 158 and 159 in FIG. 9 is exactly similar.Circuits 156 and 157 are interconnected so that they function as asingle 8-bit comparator, the outputs from pins 5-7 of circuit 157 beingfed to pins 4-2 (the cascading inputs) of circuit 156. Pin 3 of circuit157 is connected to the +5 V supply line, while pins 2 and 4 of circuit157 are grounded. Circuits 158 and 159 are arranged in exactly the samemanner as circuits 156 and 157 to form an 8-bit comparator, the outputsfrom pins 5-7 of circuit 159 being fed into the cascading inputs, pins4-2 respectively, of 158, pin 3 of 159 being connected to the +5 Vsupply line, and pins 2 and 4 of 159 being grounded.

The outputs from pins 17-14 of circuit 150, representing the four mostsignificant bits of the 8-bit last row value latched in circuit 150, arefed to pins 1, 14, 11 and 9 respectively of circuit 156. The outputsfrom pins 13-10 of circuit 150, representing the four least significantbits of the last row value, are similarly fed to pins 1, 14, 11 and 9respectively of circuit 157. The outputs from pins 9-6 of circuit 150,representing the four most significant bits of the 8-bit first row valuelatched in circuit 150, are fed to pins 1, 14, 11 and 9 respectively ofcircuit 158, while the outputs from pins 5-2 of circuit 150,representing the four least significant bits of the first row value, arefed to pins 1, 14, 11 and 9 respectively of circuit 159.

The other set of inputs to circuits 156-159 are provided from a pair ofintegrated circuits 152 and 154, each of which is a four-bit counter ofthe commercially-available 74LS93 type, the circuits 152 and 154 beinginterconnected so as to form, in effect, a single 8-bit counter. In eachof 152 and 154, pin 2 is connected to the +5 V supply line, pin 3receives the VSYNC signal (from driver 130C, pin 3 via connector CK, asdescribed above with reference to FIG. 6) and pins 12 and 1 areinterconnected so that the maximum count length could be used. Toprovide the necessary carry from circuit 154 to circuit 152, pin 11 of154 is connected to pin 14 of 152. The input to pin 14 of 154 is theinverse half-speed horizontal synchronization signal from integratedcircuit 148, pin 9 (see FIG. 8). As will be apparent to those skilled inthe art, the effect of the connection best described to circuits 152 and154 is that at the beginning of each frame of video data the 8-bitcounter formed by circuits 152 and 154 is reset to zero by the pulse insignal VSYNC. Thereafter, circuits 152 and 154 count new lines of videodata using the inverse half-speed horizontal synchronization signal astheir clock input. Thus, the 8-bit number stored in 152 and 154 at anytime represents the number of the last new line of video data in thecurrent frame.

The outputs from pins 11, 8, 9 and 12 of circuit 152, which representthe four most significant bits of the 8-bit number stored in circuits152 and 154, are supplied to pins 15, 13, 12 and 10 respectively ofcircuits 156 and 158. Similarly, the outputs from pins 11, 8, 9, and 12of circuit 154, which represent the four least significant bits of thenumbers stored in circuits 152 and 154, are supplied to pins 15, 13, and12 respectively of circuits 157 and 159.

The interconnected circuits 158 and 159 compare the 8-bit current rownumber which they receive from circuits 152 and 154 with the 8-bit firstrow value received from circuit 150. The output from pin 7 (the A lessthan B output) of circuit 158 is fed to pin 11 of integrated circuit164A. Integrated circuit 164 is a quadruple 2-input NOR gate of thecommercially-available 74LS02 type. The second input to pin 12 of 164Ais taken from pin 5 (the A greater than B output) of circuit 156. Aswill be apparent to those skilled in the art, the output from pin 7 ofcircuit 158 remains high from the beginning of each frame of video datauntil the current row value stored in circuits 152 and 154 equals thefirst row value stored in circuit 150 i.e. until the first row of thewindow is reached. When the first row is reached, the output from pin 7of circuit 158 goes low. On the other hand, the output from pin 5 ofcircuit 156 remains low from the beginning of each frame of data untilthe current row value stored in circuits 152 and 154 becomes greaterthan the last row value stored in circuit 150 i.e. until the first lineafter the window begins, then goes high. Thus, the output from pin 13 ofgate 164A, which is the end-of-frame signal EOF, will only be high whenthe video data being received from the camera relates to the selectedrows defining the window. As previously mentioned, the EOF signal issent to circuit 142A, pins 17 and 18 (see preceding description withreference to FIG. 8).

It now remains to gate the EOF signal in accordance with a row/skipvalue previously set by the operator to produce the final ACCROW signal.This row/skip value specifies the number of lines to be skipped betweeneach line to be accepted. At an appropriate point, the computer sends an8-bit number which combines the 4-bit row/skip value with the 4-bitcolumn skip value (the use of which is described below) on the computerdata bus 284 (FIG. 7), and simultaneously sends an appropriate address,XFCI, on the computer address bus 286 (FIG. 7), thereby causing the8-bit skip value on the data bus 284 to be latched in an appropriateskip register in integrating circuit 142. The row skip value appears atpins 5-2 of integrated circuit 142, as shown on section 142B in FIG. 9,and the outputs from these pins are fed to pins 1, 14, 11 and 9respectively of integrated circuit 172, which is another 74LS85 4-bitcomparator. As with circuits 157 and 159 described earlier, pin 3 ofcircuit 172 is connected to the +5 V supply line, while pins 2 and 4 aregrounded. The other set of inputs to the circuit 172 are supplied by anintegrated circuit 162, which is another 74LS93 counter. Pin 3 of 162 isconnected to the +5 V supply line, while pin thereof (the second resetinput) receives the ACROW signal, thereby ensuring that counter circuit162 is reset each time the ACCROW signal is generated. Pins 12 and 1 ofcircuit 162 are interconnected to provide for maximum count length,while pin 14 of 162 receives the half-speed horizontal synchronizationsignal, SBLNK/2 from circuit 148 pin 10 (FIG. 8). Thus, circuit 162functions in generally the same manner as circuit 154 as previouslydescribed, and counts new lines of video data. Circuit 172 compares thecurrent row value received from 162 with the row/skip value receivedfrom 142B. The output from pin 7 (the A less than B output) of circuit172 will remain high until the value stored in 162 equals the row/skipvalue, then will go low. This output from pin 7 of circuit 172 willhereinafter be referred to as the "skip/row" signal. Since so long as itremains high, the value in 162 is less than the row/skip value, thusindicating that the accept row signal, ACCROW, should not be generated.

The skip row signal from pin 7 of circuit 172 is supplied to pin 5 of164B, a second NOR gate on the 74LS02 integrated circuit 164 previouslymentioned. To provide the other input to gate 164B, the EOF signal frompin 13 of gate 164A is supplied to pin 9 of 164C, a third NOR gate onintegrated circuit 164 previously mentioned. The second input, pin 8, ofgate 164C is grounded so that 164C acts as inverter, and the output frompin 10 of 164C is supplied to pin 6, the second input, of gate 164B. Theoutput from pin 4 of 164B is supplied to pin 2 of circuit 166A.Integrated circuit 166 is a dual J-K negative edge triggered flip-flopof the commercially-available 74LS112 type. Pin 4 (the preset input) of164A is connected to the +5 V supply line, while pin 15 (the clearinput) of circuit 166A receives the signal CLR from inverter 120B, pin 6(see FIG. 8). Pin 1 of 166A (the clock input) receives the inversehalf-speed horizontal synchronization signal from circuit 148, pin 9(see FIG. 8.)

The generation of the signals supplied to pin 3 of circuit 166A israther complicated. The output from pin 10 of gate 164C is supplied topin 10 of 165A, which is part of a quadruple 2-input positive NAND dateof the commercially-available 74LS00 type. Pin 9 (the second input) ofgate 165A receives the Q output from pin 9 of 166B, which is the secondflip-flop on the 74LS112 integrated circuit 166 previously mentioned.The output from pin 8 of gate 165A is fed to pin 5 of 165B, a secondNAND gate on the same integrated circuit 165. The skip/row signal fromcircuit 172 to pin 7 is fed to pin 1 of 165C, a third NAND gate on theintegrated circuit 165 previously mentioned, the second input, pin 2, ofthis gate 165C being supplied with the Q output from pin 9 of 166B. Theoutput from pin 3 of gate 165C is fed to pin 4, the second input, ofgate 165B, and the output from pin 6 of gate 165B supplied to pin 3 of166A. The Q output from pin 6 of 166A is fed to pin 10 of 167A.Integrated circuit 167 is a dual 4-input NAND gate of thecommercially-available 74LS20 type.

166B is connected in a manner very similar to 166A. Pin 10 (the presetinput) of 166B is connected to the +5 V supply line, pin 14 (the clearinput) receives the CLR signal from inverter 120B pin 6 (FIG. 8). Pin 11(the J input) receives the EOF signal from gate 164A pin 13, pin 13 (theclock input) receives the inverse half-speed horizontal synchronizationsignal from circuit 148 pin 9 (FIG. 8) and pin 12 (the K input) receivesthe signal from pin 10 of gate 164C. The Q output from pin 9 of 166 V isfed to pin 9 of gate 167. Pin 12 of 167 receives the SBLNK/2 signal fromcircuit 148 pin 10 (FIG. 8) and pin 13 of gate 167 receives the SBLNKsignal from driver 130D, pin 9 (FIG. 6), via connector CL. The outputfrom pin 8 of gate 167 is supplied to pin 13 of 169A. Integrated circuit169 is a quadruple 2-input positive NAND gate of thecommercially-available 74LS00 type. The second input, pin 12 of gate169A is connected to the + 5 V supply line so that gate 169A acts as aninverter and the output from pin 11 of gate 169A is the accept rowsignal, ACCROW which is supplied to the row control circuitry shown inFIG. 10 and also, as previously described, to circuit 162 pin 2.)

Although the signal manipulation effected by the various gates and theflip-flops shown in the right-hand part of FIG. 9 is rather complex,those skilled in the art will be able, by following the signals passingthrough the circuitry described above, to confirm the followingconditions required for ACCROW to go high. Firstly, either EOF must behigh (i.e. the video data must be within the selected window defined bythe first and last row values) or if EOF has just gone low, ACCROW canstill be high in the first row of video data immediately following thenegative transition of the EOF signal; this "overshoot" arises becauseof the way in which the flip-flops 166A and 166B toggle outputs inresponse to the half-speed horizontal synchronization signal and becausethe circuitry uses both SBLNK/2 and its inverse. In addition, for ACCROWto be high, SBLANK and SBLANK/2 must both be high i.e. the video data donot relate to a horizontal blanking interval and do relate to a new, nota repeated line of video data; the necessary gating of the signal fromflip-flop 166A and 166B with SBLNK and SBLNK/2 is effected by gate 167A.Finally, if the row skip value latched in circuit 142 is N, for ACCROWto be high, the video data must relate to the selected one of a set ofN+1 lines; as noted above, the skip row signal from pin 7 of circuit 172remains high for N new lines of video data, then goes low for a singleline until counter circuit 162 is reset to zero by the ACCROW signalgenerated.

FIG. 10 shows the row control portion 140B of the controller board 140.The circuitry shown in the left-hand part of FIG. 10 is very similar tothat shown in the corresponding part of the column control portion shownin FIG. 9, but the subsequent gating arrangements are somewhat differentbecause there is no need to generate any signal corresponding to the EOFsignal generated by the row control circuitry, nor is there any need tomake allowance for both half-speed and full-speed synchronizationsignals, since the TN2500 video camera does not interlace columns in thesame way it interlaces rows. Storage of first and last column valuesreceived from the computer is effected by an integrated circuit 160,which is another R6520 interface identical to integrated circuit 150shown in FIG. 9. The connections to and functioning of circuit 160 areclosely similar to those of circuit 150. Pins 26-33 of circuit 160 areconnected to lines 7-0 respectively of bus 288 and are thus connectedvia buffers 112 and 144 to lines 7-0 respectively of computer data bus284 (FIG. 7). Pin 34 of 160 receives the RESET signal on line 288-24 viaconnector CZ. Pins 35 and 36 of 160 are connected to lines 9 and 8respectively of bus 288 and thus receive the two least significantdigits appearing on computer address bus 286 (FIG. 7). Pin 21 of 160receives the R/W on line 288-21 via connector CW. Pin 22 of circuit 160receives the device select signal DS from inverter 120A, pin 4 (FIG. 7),while pin 23 of circuit 160 receives the control signal CSE from circuit144B, pin 10 (see FIG. 8). Pin 24 of circuit 160 receives the controlsignal CSA from inverter 120D, pin 2 (FIG. 8). As may be seen fromconsideration of the inputs to its pins 22-24, and the inputs tocircuits 144A and 144B (FIG. 8), circuit 160 is addressed by addressesXFD4-XFD7 appearing on the computer address bus 286 (FIG. 7). Pin 25 of160 receives the φ2 signal from pin 5 of driver 130B (FIG. 7) via line288-20 and connector CV. Pins 1, 18, 19 and 20 of 160 are connected tothe +5 V supply line via a resistor R2.

Integrated circuit 160 functions in a manner exactly parallel to that ofintegrated circuit 150 described above. Upon receipt of a first address,XFD4, on the computer address bus 286 (FIG. 7), circuit 160 will latchthe first column value simultaneously appearing on computer data bus 284into a first column register, whereupon receipt of a second preselectedaddress, XFD6, on computer address bus 286, circuit 160 will latch thelast column value simultaneously being on computer data bus 284 into alast column register. Obviously, the relevant addresses which causelatching of the first and last column values into circuit 160 aredifferent from those which cause latching of first and last row valuesinto circuit 150.

The outputs from circuit 160 are handled in a manner exactly parallel tothose from circuit 150. The outputs from pins 17-14 of circuit 160,which represent the four most significant bits of the last column value,are fed to pins 1, 14, 11 and 9 respectively of integrated circuit 176.The outputs from pins 13-10 of circuit 160, which represent the fourleast significant bits of the last column value, are fed to pins 1, 14,11 and 9 respectively of integrated circuit 177. The outputs from pins9-6 of circuit 160, which represent the four most significant bits ofthe first column value latched in circuit 160, are fed to pins 1, 14, 11and 9 respectively of integrated circuit 178, and finally the outputsfrom pins 5-2 of circuit 160, which represent the four least significantbits of the first column value, are fed to pins 1, 14, 11 and 9respectively of integrated circuit 179. Each of the integrated circuits176-179 is a four-bit comparator of the commercially-available 74LS85type. Integrated circuits 176 and 177 are interconnected so as to act asan 8-bit comparator, the outputs from pins 5-7 of circuit 177 being fedto pins 4-2 respectively of circuit 176. Pin 3 of 177 is connected tothe +5 V supply line while pins 2 and 4 are grounded. Similarly,integrated circuits 178 and 179 are interconnected to act as an 8-bitcomparator, the outputs from pins 5-7 of circuit 179 being fed to pin4-2 respectively of circuit 178, pin 3 of circuit of 179 being connectedto +5 V supply line and pins 2 and 4 being grounded.

The second sets of inputs to circuits 176-179 are provided by integratedcircuits 174 and 175. However, these integrated circuits 174 and 175,unlike the corresponding circuits 152 and 154 in FIG. 9, are synchronous4-bit counters of the commercially-available 74LS161 type. Circuits 174and 175 are interconnected so as to act as a single 8-bit counter, pin15 (the carry output) of circuit 175 being connected to pin 10 (theenable T input) of circuit 174.

Pin 9 (the load input), pin 7 (the enable P input) and pins 6-3 (thedata inputs) of circuits 174 and 175 are all connected to the +5 Vsupply line. Pin 10 (the enable T input) of circuit 175 is alsoconnected to the same supply line so that circuit 175 is permanentlyenabled for counting while circuit 174 will only be enabled for countingwhen a carry output is present is pin 15 of circuit 175. Pin 1 ofcircuits 174 and 175 receives the ACCROW signal from pin 11 of gate 169A(FIG. 9), while pin 2 of circuits 174 and 175 receives the ERC signalfrom pin 12 of inverter 120E (FIG. 8).

As will be apparent to those skilled in the art, 174 and 175 will bereset to zero each time ACCROW goes low i.e. the counting by 174 and 175will begin from zero at the beginning of every accepted line of videodata, and, during each of these accepted lines, counters 174 and 175 usethe ERC signal to generate a number representing the number of the pixelwithin the accepted row to which the simultaneously-arriving video datarelates.

The outputs from pins 11, 12, 13 and 14 of circuit 174, which representthe four most significant bits of the 8-bit current pixel number storedin circuits 174 and 175 are fed to pins 15, 13, 12 and 10 respectivelyof each of circuits 17l and 178. Similarly, the outputs from pins 11,12, 13 and 14 of 175, which represent the four least significant bits ofthe current pixel number, are fed to pins 15, 13, 12 and 10 respectivelyof circuits 177 and 179.

Circuits 178 and 179 compare the current pixel value received fromcircuits 174 and 175 with the first column value received from circuit160. So long as the current pixel value is less than the first columnvalue, the output at pin 7 (the A less than B output) of circuit 178remains high, but as soon as the these two values are equal (i.e. assoon as the first pixel within the selected window has been reached)this output goes low. Similarly, circuits 176 and 177 compare thecurrent pixel value from circuits 174 and 175 with the last column valuefrom circuit 160 and once the current pixel value exceeds the lastcolumn value (i.e. as soon as the row being dealt with leaves thewindow), the output at pin 5 (the A greater than B output) circuit 176goes high.

The output from pin 7 circuit 178 is fed to pin 2 of a NOR gate 164B,which is the fourth NOR gate on the 74LS02 integrated circuit 164previously mentioned. For reasons exactly parallel to those explainedabove for the generation of the EOF signal by gate 164A (FIG. 9) in thecolumn control circuitry, the output from pin 1 of gate 164D will onlybe high within the selected window. This output from pin 1 of 164D isfed to pin 2 of 167B (the second 4-input NAND gate on the 74LS520integrated circuit 167 previously mentioned, to pin 1 of a gate 171A, topin 13 of gate 171B and to pin 4 of gate 171C. Gates 171A, 171B and 171Care three separate NAND gates on a quadruple 2-input positive NAND gateof the commercially-available 74LS00 type.

For reasons exactly parallel to those explained above with reference tothe row control circuitry, the output from pin 1 of gate 164D, whichdefines the window, must be gated with the column skip function toproduce the final accept pixel signal, ACCPIX. For this purpose, the4-bit value of the row skip function, which is latched into integratedcircuit 142 in the manner previously described, is fed from pins 9-6 ofcircuit 142 (shown in portion 142C in FIG. 10) to pins 1, 14, 11 and 9respectively of integrated circuit 182, which is another 4-bitcomparator of the commercially-available 74LS85 type. Pin 3 of 182 isconnected to the +5 V supply line, while pins 2 and 4 are grounded. Theother set of data inputs to circuit 182 are provided by an integratedcircuit 181, which is a 4-bit synchronous counter of thecommercially-available 74LS161 type. Circuit 181 is arranged in a mannerclosely similar to circuit 175 previously described; pins 10, 9 and 7-3of 161 are connected to the +5 V supply line, while pin 2 of circuit 181receives the ERC signal from inverter 120C, pin 10 (FIG. 8).

The reset input to pin 1 of circuit 181 is a NAND'ed combination ofsignals ERC and ACCPIX, generated as described below. The outputs frompins 11, 12, 13 and 14 of circuit 181 are fed to pins 15, 13, 12 and 10respectively of circuit 182. Obviously, circuit 182 compares the pixelnumber received from circuit 181 with the column skip value receivedfrom circuit 142 and produces the usual outputs of a 74LS85 comparator.

However, at this point the column control circuitry shown in FIG. 10diverages markedly from the row control circuitry shown in FIG. 9. Thedifference in circuitry is required by a difference between the forms ofthe horizontal blanking signal SBLNK and the element rate clock signalERC. As will be explained in more detail below with reference to FIG.14, SBLNK is high for the major part of each cycle during which videodata is being received and only goes low during a relatively briefhorizontal blanking interval. Because integrated circuit 148 (FIG. 8) isa positive edge triggered flip-flop, SBLNK/2 is high for the whole ofone line of video data (including the relative horizontal blankinginterval) and low for the next line (again including the relativehorizontal blanking interval). The presence of gate 167A (FIG. 9) in thecolumn control circuitry, which gates a modified form of EOF with bothSBLNK and SBLNK/2, ensures that the positive and negative transitions ofACCROW are synchronized with the corresponding transitions of SBLNK.Furthermore, because of the way in which the comparators 156-159 and thegate 164A (FIG. 9) operate, the negative transition of EOF at the end ofthe window corresponds with positive transitions in SBLNK and SBLNK/2.Following such a negative transition of EOF, the presence of theflip-flops 166A and 166B permits a final high pulse in ACCROW, thisfinal pulse (earlier referred to as the "overhang" beginning with thepositive transition of SBLNK which coincides with the negativetransition in EOF, and terminating with the immediately followingnegative transition in SBLNK. Thus, all high-level pulses of a ACCROWare correctly synchronized with high-level pulses of SBLNK.

In contrast, because there is no blanking interval between adjacentpixels comparable to the horizontal blanking interval between adjacentrows, ERC undergoes one complete cycle for each pixel, this cyclecomprising a low value for the first half of the period for which videodata from that pixel is present, and a high value for the second half ofthe same period. Similarly, ERC, the inverse signal which is actuallycounted by circuits 174 and 175 (FIG. 10) is high for the first half ofeach output pixel period and low for the second half. Since it isimportant that the accept pixel signal remain high for the whole of thetime for which video data from the accepted pixel are to be received inorder to permit the memory board the maximum time to store the videodata to be accepted (as already mentioned, since ERC has a frequency ofapproximately 4.5 MHz, the data from any given pixel is only presentfrom about 0.22 microseconds, and any further reduction in this periodis likely to cause extreme problems in storing the video data from theaccepted pixel in the memoreis of the video-computer interface). Thus,the positive transition of ACCPIX must correspond with the positivetransition of ERC denoting the start of the video data from the first ofan accepted set of pixels, while the negative transition of ACCPIX doesnot correspond with a negative transition in ERC but rather with apositive transition in ERC which denotes the end of the last pixel tothe accepted and the beginning of the subsequent pixel. In particular,ACCPIX is allowed to "overshoot" the end of signal 164-1 (the outputfrom pin I of gate 164D in FIG. 10, the column control equivalent ofsignal EOF) in the same way that ACCROW is allowed to "overshoot" EOFi.e. after 164-1 goes low, because of the presence of flip-flops 173Aand 173B (FIG. 10) described below, the next pixel following thenegative transition of 164-1 can still be accepted. In the case of thislast pixel, the negative transition of ACCPIX must be arranged tocoincide not with the negative transition of ERC but with the firstpositive transition in ERC immediately following the positive transitionwhich coincides with the negative transition in 164-1.

To produce an ACCPIX signal meeting the aforementioned requirements, thecircuitry shown in FIG. 10 makes use of two different skip columnsignals, hereinafter designated skip column A and skip column B; this isof course in contrast to the row control circuitry shown in FIG. 9 whichuses only a single skip row signal from pin 7 of circuit 172. The skipcolumn A signal is the output from pin 6 (the A=B output) of comparator182, while the skip column B signal is the output from pin 7 (the A lessthan B output) of the same comparator. As will be apparent to thoseskilled in the art, the negative transitions in the skip column A andskip column B signals will be spaced apart by one pixel period, thenegative transition of the skip column B signal (and the positivetransition of the skip column A signal) will coincide with the positivetransition in ERC for the pixel which causes the number accumulated incircuit 181 to equal the column skip value appearing at pins 9-6 ofcircuit 142C, while the negative transition in the skip column A signalwill coincide with the immediately subsequent positive transition inERC, denoting the start of the following pixel.

The output from pin 1 of gate 164D (signal 164-1) is fed to pin 2 ofgate 167B, which is the second 4-input NAND gate on the 74LS20integrated circuit 167 previously mentioned. Pin 4 of 167B is connectedto the positive supply line, pin 5 receives the skip column B signalfrom pin 7 of comparator 182, and pin 1 of gate 167B receives the Qoutput from flip-flop 173B described below. The output from pin 6 ofgate 167B is fed to pin 10 of 169B, which is a further NAND gate on the74LS00 integrated circuit 169 previously mentioned. The second input,pin 9, of gate 169B is connected to the +5 V supply line so that gate169B acts as an inverter. The output from pin 8 of gate 169B is fed topin 3 of flip-flop 173A. Integrated circuit 173 is a dual J-Knegative-edge triggered flip-flop of the commercially-available 74LS112type. Pins 4 and 15 (the preset and clear inputs) of 173A are bothconnected to the positive supply line. Pin 1 (the clock input) of 173Areceives the ERC signal. Pin 1 of gate 164D is also connected to pin 2of 171. Integrated circuit 171A is a quadruple 2-input positive NANDgate of the commercially-available 74LS00 type. The other input to pin 1of gate 171A is the skip column B signal from pin 7 of comparator 182.The output from pin 3 of gate 171A is fed to pin 2 (the K input) offlip-flop 173A.

The Q output from pin 6 of flip-flop 173A is fed to pin 12 of 171B,which is a second NAND gate on the 74LS00 integrated circuit 171previously mentioned. The other input to pin 13 of 171B is signal 164-1from gate 164D, pin 1. The output from pin 11 of gate 171B is fed to pin10 of 171D, which is another NAND gate on the same integrated circuit.Signal 164-1 from pin 1 of gate 164D is supplied to pin 4 of 171C,another NAND gate of the 74LS00 integrated circuit 171 previouslymentioned. The other input to pin 5 of gate 171C is the skip column Asignal from pin 6 of comparator 182. The output from pin 6 of gate 176Cis supplied to second input, pin 9, of gate 171D and the output from pin8 of gate 171D is supplied to pin 11 (the J input) of 171B, which is thesecond flip-flop on the 74LS112 integrated circuit 173 previouslymentioned. Pin 13 (the clock input of flip-flop 173B receives the ERCsignal from pin 12 of inverter 120E (FIG. 8). Pins 14 and 10 (the clearand preset inputs) of flip-flop 173B are connected to the positivesupply line.

The Q output from pin 9 of flip-flop 173B is fed to pin 4 of 169C, whichis a third NAND gate on the 74LS00 integrated circuit 169 previouslymentioned. The other input to pin 5 of gate 169C is the Q output frompin 6 of flip-flop 173A. The output from pin 6 of gate 169C is fed topin 11 of 120B which is a second inverter on the 74LS04 integratedcircuit 120 previously mentioned. The inverted output from pin 10 ofinverter 120B is the ACCPIX signal having the characteristics previouslymentioned. It should be noted that, because the gate 169C merely NAND'sthe outputs from flip-flops 173A and 173B, and does not effect gatingwith ERC in the same way that gate 167A effects gating with SBLNK andSBLNK/2, provided the row skip function is set to zero so that everypixel on an accepted line and lying within the window is to be accepted,once ACCPIX has gone high at the first accepted pixel it does notthereafter go low until the end of the last accepted pixel, as describedbelow in more detail with reference to FIG. 14A.

To provide proper resetting of the counter circuit 181, the ACCPIXsignal from pin 10 of inverter 120B is fed to pin 2 of 169D, the fourthNAND gate on the 74LS00 integrated circuit 169 previously mentioned. Thesecond input to pin 1 gate 169D is the ERC signal from inverter 120C,pin 12 (FIG. 8). The output from pin 3 of gate 169D is fed to pin 1 ofcounter circuit 181.

The ACCPIX signal from pin 10 of inverter 120B is fed to connectors CNand CU for passage to the memory board 274 and the analog board 280respectively, as described above with reference to FIG. 6.

The circuitry of the memory board 274 will now be described withreference to FIGS. 11 and 12. In FIG. 11, integrated circuits 186, 188and 190 are three 4-bit synchronous counters of thecommercially-available 74LS161 type. As will be apparent to thoseskilled in the art, as 8-bit numbers representing video data fromaccepted pixels are fed to the video-computer interface via the bus 306(FIGS. 4, 5 and 12) it is necessary to generate addresses to advise thememory of the video-computer interface of the various locations in whichthe incoming video data should be stored. Generation of the necessaryaddresses is affected by integrated circuits 186, 188 and 190, which areinterconnected so as to generate the 12-bit addresses required by the 4Kmemory described below. Pins 3, 4, 5 and 6 (the four data inputs) andpin 9 (the load input) of each of 186, 188 and 190 are all held highbeing connected to the +5 V supply line. Pin 1 (the clear input) of eachof 186, 188 and 190 receives the CLR signal from inverter 120B, pin 6(FIG. 8) via connectors CP and MP, as described above with reference toFIG. 6. This feeding of CLR to the clear input of each of circuits 186,188 and 190 ensures that all three counters are zeroed at the beginningof each frame of video data. To provide the clock input to circuits 186,188 and 190, the ERC signal from driver 130E pin 11 (FIG. 6) viaconnector MM is fed to pin 1 of 202A. Integrated circuit 202 is a hexinverter of the commercially-available 74LS04 type. The inverted outputfrom pin 2 of inverter 202A is fed to pin 2 of 198A. Integrated circuit198 is a quadruple 2-input AND gate of the commercially-available 74LS08type. The second input to pin 1 of gate 198A is the ACCPIX signal frompin 10 of inverter 120E, received via connectors CN, as described abovewith reference to FIG. 6. The output from pin 3 of gate 198A furnishesthe clock input to pin 2 of each of circuits 186, 188 and 190.

Pins 10 and 7 (the two enable inputs) of circuit 190 are connected tothe +5 V supply line so that circuit 190 is always enabled. The carryoutput from pin 15 of circuit 190 is fed to pin 7 (the enable P input)of circuit 188, pin 10 (the enable T input) of circuit 188 beingconnected to the +5 V supply line. The carry output from pin 15 ofcircuit 188 is fed to pin 10 (the enable T input) of circuit 186, whilepin 7 (the enable P input) of circuit 186 receives the carry output frompin 15 of circuit 190. As will be apparent to those skilled in the art,the provision of gate 198A ensures that the counter circuits 186, 188and 190 only count when the ERC signal is low and the ACCPIX signal ishigh, so that the counters count accepted pixels of video data.Furthermore, it will be apparent to those skilled in the art thatwhereas circuit 190 is permanently enabled, circuit 188 will be enabledonly when a carry output is present at pin 15 of circuit 190 and thatcircuit 186 will be enabled only when carry outputs are simultaneouslypresent at pins 15 of circuits 188 and 190. Thus, since circuits 186,188 and 190 are reset by the CLR signal at the beginning of each frameof video data, as successive pixels are accepted the 12-bit numberrepresented by the outputs of circuits 186, 188 and 190 will beincremented each time a pixel is accepted.

The outputs from pins 11-14 of circuit 186 (which represent the fourmost significant bits of the 12-bit address number generated by circuits186, 188 and 190) are fed to pins 2, 5, 14 and 11 respectively of anintegrated circuit 192. Similarly, the outputs from pins 11-14 ofcircuit 188 (which represent the four middle bits of the aforementioned12-bit address) are fed to pins 2, 5, 14 and 11 respectively ofintegrated circuit 194, and to the outputs from pins 11-14 of circuit190 (which represent the four least significant bits of theaforementioned 12-bit address) are fed to pins 2, 5, 14 and 11respectively of an integrated circuit 196. Integrated circuits 192, 194and 196 are each a Schottky quadruple 2-input 3-state multiplexer of thecommercially-available 74LS257 type. Pin 1 (the select input) of each ofcircuits 192, 194 and 196 is provided with the COM/CAM signal from pin10 of circuit 142A (FIG. 8) received via line 304 and connectors CR andMR, as described above with reference to FIG. 6.

The second set of inputs to each of the multiplexer circuits 192, 194and 196 is provided from lines 19-8 of bus 288; as explained above withreference to FIG. 7, these lines 19-8 of bus 288 carry signalscorresponding to the 12 least significant bits on the computer addressbus 286, buffered via the buffers 122 and 126. Pins 3, 6, 13 and 10 ofcircuit 192 are connected to lines 19-16 respectively of bus 286, andthus receive signals corresponding to those on lines 11-8 respectivelyof computer address bus 286. Similarly, lines 3, 6, 13 and 10 of circuit194 are connected to lines 15-12 respectively of bus 288 and receivesignals corresponding to lines 7-4 respectively of computer address bus286, while pins 3, 6, 13 and 10 of circuit 196 are connected to lines11-8 respectively of bus 288 and thus receive signals corresponding tolines 3-0 of computer address bus 286.

Multiplexer circuits 192, 194 and 196 serve to permit both the computeraddress bus 286 and the 12-bit counter formed by circuits 186, 188 and190 to furnish addresses to the memories of the memory board. WhenCOM/CAM goes low, indicating that the computer has instructed theinterface to acquire video data, the outputs of circuits 192, 194 and196 track the inputs thereto from circuits 186, 188 and 190respectively, whereas when COM/CAM goes high the outputs from circuits192, 194 and 196 will track the inputs from bus 288, and thus the twelveleast significant bits on the computer address bus 286.

As already mentioned, the memories used in the video-computer interfacepresently being described are too slow to acquire video data at the rateat which it is being received, and accordingly special circuitry is usedso that one or other of two different memories is enabled, dependingupon whether the 12-bit address represented by the outputs from circuits192, 194 and 196 is odd or even i.e. depending upon whether the leastsignificant bit (the output from pin 9 of circuit 196) is a 1 or 0.Accordingly, the outputs from pins 4, 7, 12 and 9 of circuit 192(representing the four most significant bits of the 12-bit address to beused by the memories) are supplied to pins 2, 3, 6 and 7 respectively ofeach of a pair of integrated circuits 210 and 216. Similarly, theoutputs from pins 4, 7, 12 and 9 of circuit 194 (representing the fourmiddle bits of the 12-bit address) are fed to pins 2, 3, 6 and 7respectively of a pair of integrated circuits 212 and 218. The outputsfrom pins 4, 7 and 12 of pin 196 (representing bits 3, 2 and 1 of the12-bit address) are similarly fed to pins 2, 3 and 6 respectively of apair of integrated circuits 214 and 220. Each of circuits 210, 212, 214,216, 218 and 220 is a 4-bit bistable latch of the commercially-available74LS75 type. As will be described in more detail below, circuits 210,212 and 214 are arranged to act, in effect, as a single 10-bit latchwhich is enabled when the address from circuits 192, 194 and 196 is odd,subject to certain other conditions described below, and similarly,circuits 216, 218 and 220 are arranged to act as a single 10-bit latchwhen the address is even, subject to the same conditions.

To allow for proper enablement of the latch circuits 210-220, the outputfrom pin 9 of circuit 196, representing the least significant bit of theaddress provided circuits 192, 194 and 196, is passed to pin 9 of 202B,which is a second inverter on the 74LS04 integrated circuit 202 alreadymentioned. The output from pin 9 of circuit 196 is also placed on a line223 for purposes described below. The inverted output from pin 8 of 202Bis passed to pin 9 of 201A. Integrated circuit 201 is a quadruple2-input positive NAND gate of the commercially-available 74LS00 type.The second input to pin 10 of gate 201A is the ACCPIX signal from pin 10of inverter 120E (FIG. 10) received via connectors CN and MN, asdescribed above with reference to FIG. 6. The output from pin 8 of gate201A is fed to pin 12 (the D input) of 208A. Integrated circuit 208 is adual positive-edge-triggered flip-flop of the commercially-available74LS74 type. Pin 11 (the clock input of flip-flop 208A) receives the ERCsignal from pin 11 of driver 130E via connector MM, as described abovewith reference to FIG. 6. Pins 10 and 13 (the preset and clear inputs)of flip-flop 208A are connected to the +5 V supply line. The Q outputfrom pin 9 of flip-flop 208A is fed to pin 5 of integrated circuit 206,which is a data selector/multiplexer of the commercially-available74LS157 type. The Q output from pin 8 of flip-flop 208A is fed to pin 11of circuit 206.

The output from pin 9 of circuit 196, representing the least significantbit of the address, is fed to pin 13 of 201B, a second NAND gate onintegrated circuit 201 already mentioned. The second input to pin 12 ofgate 201B is the ACCPIX signal from connector MN. The output from pin 11of gate 201B is fed to pin 2 (the D input) of 201B, which is the secondflip-flop on the 74LS74 integrated circuit 208 already mentioned. Pin 3(the clock input) of flip-flop 208B receives the ERC signal from theconnector MM, while pins 1 and 4 (the clear and preset inputs) offlip-flop 208B are grounded. The Q output from pin 5 of flip-flop 208Bis fed to pin 2 of integrated circuit 206, while the Q output from pin 6of flip-flop 208B is fed to pin 14 of circuit 206.

Pins 3 and 6 of circuit 206 are connected to the +5 V supply line. Pin13 receives the output from pin 9 of circuit 196, while pin 10 receivesthe corresponding inverted signal from pin 8 of inverter 202B. Pin 1(the select input) of circuit 206 receives the COM/CAM signal from line304 via connector MR. To produce the input to pin 15 (the strobe input)of circuit 206, the device select signal DS received from pin 4 ofinverter 120A (FIG. 7) via line 290 and connector MU is fed to pin 1 of201C, which is a third NAND gate on the 74LS00 integrated circuit 201previously mentioned. The second input to pin 2 of gate 201C is thememory inhibit signal, MI, from pin 8 of gate 124 (FIG. 7) received vialine 292 and connector M10, as described above with reference to FIG. 6.The output from pin 3 of gate 201C is fed to pin 10 of 198B, a secondAND gate on the 74LS08 integrated circuit 198 previously mentioned. Thesecond input to pin 9 of gate 198B is the COM/CAM signal from line 304,and the output from pin 8 of gate 198B is fed to pin 15 (the strobeinput) of circuit 206.

The output from pin 4 of circuit 206 is a latch odd signal which enablescircuits 210, 212 and 214. Similarly, the output from pin 7 of circuit206 is a latch even signal which enables 216, 218 and 220. Although thecircuitry in the middle part FIG. 11 is somewhat complicated, thoseskilled in the art will readily be able to derive the conditions forgeneration of these latch odd and latch even signals. In particular,since the inputs DS and MI to gate 201C will only both go high when themost significant hexadecimal digit on the computer address bus is thepreselected one requiring action by the interface, and when that addressis not one of the 64 reserved addresses which indicate action by theinterface other than writing to memory, the output from gate 201C (whichis an enable signal and is placed on a line 221 for purposes to bedescribed below) will only go low for the 4032 unreserved addresses.Accordingly, the output from gate 198B will only go high (disenablingcircuit 206 and locking all its outputs low) when one of the 64 reservedaddresses is involved and when COM/CAM is high, the latter conditionindicating that the computer wishes to receive video data from theinterface. This serves to prevent reading of data from the reservedaddresses in the memory. Except for blocking of the 64 reservedaddresses, when COM/CAM is high, the feeding of this signal to theselect input of pin 1 will cause the outputs at pins 4 and 7 to trackthe corresponding high inputs at pins 3 and 6, thereby generatingsimultaneous latch odd and latch even signals and enable the computer toread all the video data stored in the memories.

When COM/CAM is low, indicating that the computer wishes the interfaceto acquire video data, the situation is more complicated and the overallresult is that provided ERC is following its usual alternating pattern,indicating that the camera is actually sending video data to theinterface, and ACCPIX is high, indicating the video data relates to anaccepted pixel, when the output from pin 9 of circuit 196 goes high,indicating an odd address, pin 4 of circuit 206 will go low while pin 7will go high, thereby generating a latch odd but not a latch evensignal. On the other hand, when the output from pin 9 of circuit 196 islow, indicating an even address, pin 4 of circuit 206 will go high andpin 7 will go low, thereby generating a latch odd but not a latch evensignal. However, because the flip-flops 208A and 208B arepositive-edge-triggered and receive ERC at their clock inputs, togglingof the outputs of those flip-flops is synchronized with the positivetransitions of ERC, which occur half-way through each pixel period.Accordingly the transitions between latch odd and latch even signals layone-half of a pixel period behind the corresponding transitions in thesignal from pin 1 of circuit 196, for reasons which will be discussedbelow with reference to FIG. 14B.

The latch odd signal from pin 4 of circuit 206 is fed to pins 4 and 13(the two enable inputs) of each of circuits 210, 212, and 214. The latchodd signal from pin 4 of circuit 206 is also placed on a line 213 forpurposes described below. When the latch odd signal is high, thecircuits 210, 212 and 214 are thus enabled, the outputs from pins 16,15, 11 and 9 each of circuits 210 and 212 and from pins 16 and 15 ofcircuit 214, which represent the 10 most significant bits of the 12-bitaddress furnished by circuits 192, 194 and 196, are placed on lines 11-2of an odd bus 211. When the latch odd signal goes low, the existingaddress is latched on bus 211. Similarly, the latch even output from pin7 of circuit 206 is fed to pins 4 and 13 of each of circuits 216, 218and 220 so that when this latch even signal goes high the output frompins 16, 15, 11 and 9 of each of circuits 216 and 218 and from pins 16and 15 of circuit 220 will correspond to the ten most significant bitsof the address furnished by the circuits 192, 194 and 196, and theseoutputs are placed on lines 11-2 of an even bus 215; when the latch evensignal goes low, this existing address is latch on bus 215. The latcheven signal from pin 7 of circuit 206 is also placed on a line 217 forpurposes to be described below.

The output from pin 11 of circuit 214 representing the inverse of thesecond least significant bit of the address output by 214, is fed to pin1 of 207A. Integrated circuit 207 is a quadruple 2-input positive NANDgate of the commercially-available 74LS00 type. The output from pin 10,representing the second least significant bit of the address, is fed topin 4 of a further gate 207B on the same integrated circuit 207. Thesecond input to these two gates, pin 2 of gate 207A and pin 5 of 207B,taken from pin 12 of circuit 206. In a generally similar manner, theoutput from pin 11 of 220 is fed from pin 12 of a gate 207C on the sameintegrated circuit 207, and the output from pin 10 of circuit 220 fed topin 9 of a further gate 207B on the same integrated circuit. The secondinputs to these two gates, to pin 13 of gate 207C and pin 11 of gate207D, are taken from pin 9 of circuit 206. The outputs from pin 6 atgate 207B, pin 11 of gate 207C, pin 3 of gate 207A and pin 8 of gate207D are placed on lines 1-4 respectively of a memory enable bus 219.When the interface is applying video data, only one of the lines of thebus 219 will go low at any time, the number of the line which goes lowbeing determined by the last two bits of the address furnished fromcircuit 196, and the transitions between memory enable signals beingdelayed relative to the corresponding changes at pin 12 and 9 of circuit196 by one-half of a pixel period for reasons explained above withreference to the latch odd and latch even signals.

In FIG. 12, integrated circuits 236, 238, 240, 242, 244, 246, 248 and250 are memory chips of the commercially-available 2114 type. Pins15-17, 1-4 and 7-5 of each of memory circuits 236, 238, 244 and 246 areconnected to lines 11-2 respectively of odd bus 211 and thus receive10-bit addresses when the latch odd signal goes high. Similarly, pins15-17, 1-4 and 7-6 of memory circuits 240, 242, 248 and 250 areconnected to lines 11-2 respectively of even bus 215 and receive 10-bitaddresses when the latch even signal goes high. (For simplicity, pinnumbers of shown only on memory circuit 236. The spatial layout of pinsin FIG. 12 is identical on the other seven memory circuits.) Pin 8 ofcircuits 236 and 244 are connected to line 4 of memory enable bus 219,pin 8 of circuits 238 and 236 to line 3 of the same bus, pin 8 ofcircuits 240 and 248 to line 2 of the same bus, and pin 8 of circuits242 and 250 to line 1 of the same bus. Since, as already mentioned, onlyone line of bus 219 will go low at any one time, it will be seen thatthe memory circuits are used in four pairs, namely 236/244, 238/246,240/248, and 242/250, the pair being enabled at any one time beingdetermined by which of the lines of bus 219 goes low.

To control the direction of data flow into and out of the memories (i.e.to control whether the memories are being written into, or read from)the COM/CAM signal (on line 304, received via connector MR) and the R/Wsignal (from pin 13 of driver 130A (FIG. 7) via line 288-21 andconnector MW, as described above with reference to FIG. 6) are fed tothe two inputs of 198C, which is a third AND gate on the 74LS08integrated circuit 198 previously mentioned. The output from gate 198Cis fed to pin 10 of each of the memory circuits 236-250. Thus, toproduce writing of data into the memories, both COM/CAM and R/W must golow; if either signal goes high, reading from the memory circuits canoccur.

The aforementioned circuitry for supplying addresses, and enable andselect inputs to the memory circuits 236-250 is relativelystraightforward. The circuitry in the left-hand part of FIG. 12, whichhandles data flow to and from the memory circuits 236-250 is rather morecomplicated, for a number of reasons. Firstly, the memory circuits mustbe able to both receive video data from the camera data bus 306 andoutput video data to the computer data bus 284 (FIG. 7) via the bus 288,line 7-0 (writing of data from the computer data bus into the memories,which permits the memories to act as auxiliary memories for thecomputer, is possible e.g. for testing purposes, but is not required fornormal operation of the interface). Secondly and more importantly, asalready mentioned the video data for any pixel only remains on the bus306 for approximately 0.22 microseconds, an interval which isinsufficient to permit the enabled pair of memory circuits to acquirethe video data. Accordingly, in accordance with the special datahandling techniques of the invention, excessive 8-bit set of video dataarriving on the bus 306, each set representing the intensity of onepixel, are latched alternately on a pair of latches 224 and 232. Thus,the video data from each pixel remains on the latches for longer thanthe time it is present on the bus 306, giving the memory circuits timeto acquire the video data from the latches.

More specifically, lines 7-0 of bus 306 are connected to pins 18, 17,14, 13, 8, 7, 4 and 3 respectively of each of integrated circuits 224and 232. Integrated circuits 224 and 232 are each an octal D-type latchof the commercially-available 74LS373 type, and for simplicity pinnumbers are shown only on circuit 224; the spatial layout of pins inFIG. 12 is identical for both circuits. Pin 1 of circuits 224 and 232(the output control) receives the COM/CAM signal from line 304 viaconnector MR; thus, output from these latches will only occur whenCOM/CAM is set low by the computer, thereby instructing the interface toacquire video data from bus 306. Pin 11 of circuit 224 (the enable latchinput) receives the latch odd signal on line 213 from pin 4 of circuit206 (FIG. 11), while pin 11 of circuit 232 receives the latch evensignal from pin 7 of circuit 206 via line 217. Since, as explainedabove, when the interface is set to acquire video data and thecontroller board produces the signal ACCPIX indicating that the pixelfrom which video data is being receives is one for which retention ofthe video data is required, the latch odd and latch even signals aregenerated alternately for successive accepted pixels, the effect of theaforementioned connections to pins 7 of circuits 224 and 232 is that thedata arriving on bus 306 from pixels for which the data is to beretained, will be latched alternately in circuits 224 and 232, and sincewhile video data is being acquired, the output controls (pin 1) ofcircuits 224 and 232 are continuously held low, the video data thuslatched in 224 and 232 will be continuously present on the outputsthereof.

The outputs from pin 19, 16, 15 and 12 of circuit 224, representing thefour most significant bits of the 8-bit video data latched in 224 aresent to pins 14-11 respectively of memory circuits 236 and 238.Similarly, the outputs from pins 9, 6, 5 and 2 of circuit 224,representing the four least significant bits of the video data latchedin 224, are fed to pins 14-11 respectively of memory circuits 244 and246. In an exactly similar manner, the outputs from pins 19, 16, 15 and12 of circuit 232 are fed to pins 14-11 respectively of memory circuits240 and 244, while the outputs from pins 9, 6, 5 and 2 of circuit 232are fed to pins 14-11 respectively of memory circuits 248 and 250. Thus,each 8-bit piece of video data latched in 224 and 232 is split forstorage, the four most significant bit being stored in the enabled oneof memory circuits 236-242 and the four least significant bits stored inthe enabled one of memory circuits 244-250.

Communication between the memory circuits 236 and 250 and lines 7-0 ofbus 288 (which, as explained above with reference to FIG. 7, are intwo-way communication with the similarly-numbered line of the computerdata bus 284) is effected by four integrated circuits 222, 226, 228 and230, each of which is a type 8T28 buffer manufactured by Signetics Corp.Again, for convenience, pin numbers are shown only on circuit 222; thespatial layout of the pins on all four circuits 222, 226, 228 and 230 isidentical in FIG. 12.

Line 288-7 is connected to pins 2 and 4 of circuits 222 and 228. Line228-6 is connected to pins 14 and 12, line 228-5 to pins 5 and 7 andline 228-4 to pins 11 and 9 of the same pair of circuits 222 and 228.Similarly, line 288-3 is connected to pins 2 and 4, line 288-2 to pins14 and 12, line 288-1 to pins 5 and 7 and line 288-0 to pins 11 and 9 ofeach of the circuits 226 and 230.

Output and direction control for circuitry 222, 226, 228 and 230 isestablished by the circuitry shown in the lower left-hand portion ofFIG. 12. The enable signal from pin 3 of gate 201C (see FIG. 11) ispassed via line 221 to pin 2 of 234A. Integrated circuit 234 is a dual1-of-4 decoder/demultiplexer of the commercially-available 74LS139 type.Pin 3 of circuit 234A receives the φ2 signal from pin 5 of driver 130B(FIG. 7) via line 288-20 and connector MV. Pin 2 of 234A receives theCOM/CAM signal from line 304 via connector MR. Pin 7 of circuit 234A isconnected to pin 15 of circuit 234B, which is the seconddecoder/demultiplexer on the integrated circuit 234. Pin 14 of 234Breceives the signal from line 223, representing the output from pin 9 ofcircuit 196 (FIG. 11). Pin 13 of circuit 234B is the R/W signal from pin13 of driver 130A (FIG. 7) via line 288-21 and connector MW. The outputfrom pin 9 of 234B is fed to pin 1 (the enable input of buffer circuits222 and 226. The output from pin 10 of 234B is similarly fed to pin 1 ofcircuits 228 and 230. The output from pin 11 of 234B is fed to pin 3 of202C, which is a third inverter on the 74LS04 integrated circuit 202already mentioned, and the corresponding inverted output from pin 4 of202C is fed to pin 15 circuits 222 and 226. Finally, the output from pin12 of 234B is fed to pin 5 of 202D, a fourth inverter on the 74LS4integrated circuit 202 already mentioned, and the corresponding invertedoutput from pin 6 of 202D is fed to pins 15 of circuits 228 and 230.

Those skilled in the art will appreciate that the affect of theintegrated circuit 234 and inverters 202C and 202D is as follows. Unlessthe enable input to pin 15 of 234B is low, all the outputs of 234B willgo high and all four buffer circuits 222, 226, 228 and 230 will bedisabled. This enable input to pin 15 will only go low when the outputfrom pin 7 of 234A goes low, which will only occur when the followingconditions are simultaneously present:

A. The enable signal on line 221 is low, indicating that the addressappearing on the computer address bus 286 is not one of the 64 reservedaddresses previously mentioned;

B. The φ2 signal is high, indicating that the computer is in a positionto accept data; and

C. The R/W signal is high, indicating that the computer has asked thevideo computer interface to supply video data from its memories to thecomputer. When all three of the above conditions are fulfilled, and thesignal on line 223 is high (i.e. the last bit of the address generatedby circuit 196 (FIG. 11) is a 1, and thus the address is odd), theoutput from pin 9 of 234B goes low, while the outputs at pins 10, 11 and12 remain high. Thus, pin 1 of buffer circuits 222 and 226 goes low, andsince the output from pin 11 of 234B is still high, the inverse of thisoutput supplied to pins 15 of buffer circuits 222 and 226 also goes low.With the inputs to pins 1 and 15 of buffer circuits 222 and 226 bothlow, these two buffer circuits are enabled and read video data from theenabled pair of memory circuits 236/244 or 248/246 onto lines 7-0 of bus288, thereby transmitting video data from these memory circuits to thecomputer. Since the output from pin 10 of 234B is still high, buffercircuits 228 and 230 are not enabled and no reading takes place frommemory circuits 240, 242, 248 and 250.

If, on the other hand, the signal on line 223 is low, indicating thatthe least significant bit of the address is a 0 and thus that theaddress is even, the output from pin 10 of 234B goes low, while theoutputs at pins 9, 11, 12 of 234B remain high, thus causing reading ofdata from the enabled pair 240 and 248 or 242 and 250 of the memorycircuits via enable buffer circuits 228 and 230 onto line 7-0 of bus 288and thence to the computer data bus 284, while buffer circuits 222 and226 are disabled.

The circuity of the analog board 280 will now be described withreference to FIGS. 13A and 13B. In FIG. 13A, integrated circuit 300 is aRockwell 6520 Peripheral Interface Adapter similar to the integratedcircuits 150 and 160 described above with reference to FIGS. 9 and 10.Circuit 300 is connected in a manner similar to that of circuit 150.Pins 26-33 of circuit 300 are connected to lines 7-0 of bus 288 and thusreceive either data from the computer sent via computer data bus 284(FIG. 7), as described below with reference to block 650 in FIG. 17. Infact, the major purpose of circuit 300 is to acquire such video datafrom bus 288, to latch it in its internal registers and thereafter tooutput this data to one of the two digital/analog converters describedbelow for conversion to analog form and forwarding to the oscilloscope76, as described in more detail below. Pin 21 of circuit 300 receivesthe R/W signal from line 288-21 via connector AW, while line 22 receivesthe DS signal from line 290 via connector AF. Pin 23 of circuit 300receives the control signal CSF from circuit 144B, pin 9 (FIG. 8) andpin 24 of circuit 300 receives the control signal CSA from pin 2 ofinverter 120D (FIG. 8). Thus circuit 300 is addressed by addressesXFDC-XFDF. Pin 25 of circuit 300 receives the φ2 signal from pin 5 ofdriver 130B (FIG. 7) via line 288-20 and connector AV. Pin 34 of circuit300 receives the RESET signal from the computer via line 287-7, line288-24 and connector AZ. Pins 35 and 36 of circuit 300 are connected tolines 9 and 8 respectively of bus 288 and thus receive the two leastsignificant bits appearing on the computer address bus 286 (FIG. 7).Pins 18, 19, 39 and 40 of circuit 300 are connected to the +5 V supplyline via a resistor R3, while pin 1 is grounded via connector AA.

The outputs from pins 17-10 of circuit 300 (port B in the manufacturer'snomenclature) are fed to pins 5-12 respectively of an integrated circuit302. Similarly, the outputs from pins 9-2 of circuit 300 (port A in themanufacturer's nomenclature) are fed to pins 5-12 respectively ofintegrated circuit 304. Integrated circuits 302 and 304 are 8-bitdigital/analog converters of the commercially-available 1408 type,manufactured by Motorola.

Pins 1 and 2 of circuits 302 and 304 are grounded. Pin 15 of circuit 302is connected to the ground line (connector AA) via a resistor R4 and pin15 of circuit 304 is similarly grounded by a resistor of 5. The -12 Vsupply line (connector AJ) is connected via a capacitor C1 to ground,via a capacitor C2 to the ground connector AA and directly to pin 3 ofcircuits 302 and 304. Pins 3 and 15 of each of circuits 302 and 304 areinterconnected via capacitors C4 and C5 respectively.

Pin 13 of circuits 302 and 304 is connected to the +5 V supply line viaconnector AB, stabilization of the +5 V inputs to these pins 13 beingachieved by capacitors C6 and C7 connected between the +5 V supply lineand ground. The +5 V supply line is also connected to pin 1 of a powersupply integrated circuit 306, which of the commercially-availableMotorola 1403 type pin 3 of circuit 306 is grounded, pins 1 and 3 arebridged by a capacitor C8 and pins 3 and 2 are bridged by a capacitorC9. The output from pin 2 of circuit 306 is fed via a fixed resistor R6and a variable resistor R7 connected in series to pin 14 of circuit 302,and is also fed via a fixed resistor R8 and a variable resistor R9connected in series to pin 14 of circuit 304.

The analog output from pin 4 of circuit 302 is fed to pin 2 of anintegrated circuit 308, which is a type CA 3100 analog amplifiermanufactured by RCA. The positive input to pin 3 of amplifier 308 istaken from the ground connector AA, this ground connector beingconnected to the -12 V supply line (connector AJ) via a capacitor C10.Amplifier 308 receives the conventional power connections, +12 V fromconnector AR at pin 7 and -12 V from connector AJ at pin 4; note thatthe +12 V supply line is connected to ground via capactor C11. Theanalog output from pin 6 of amplifier 308 is passed via a resistor R10to connector AK and thence via one of the lines 86 to the oscilloscope76, as described above with reference to FIG. 6. To provide feedback forthe amplifier 308, pins 6 and 2 thereof are bridged by a capacitor C12,while the terminal of R10 remote from the amplifier 308 is connected topin 2 of the amplifier via resistor R11.

The analog output from pin 4 of circuit 304 is treated in an exactlyparallel manner, being fed to pin 2 of an amplifier 310, which is afurther CA3100 amplifier identical to amplifier 308 just described.Amplifier 310 receives connections at pins 3, 4 and 7 identical to thecorresponding connections to amplifier 308 and its analog output frompin 6 is sent via a resistor R12 to connector AL and thence via thesecond line 86 to the oscilloscope 76, as described above with referenceto FIG. 6. Amplifier 310 is provided with a feedback capacitor C13 and afeedback resistor R14 connected in a manner exactly parallel to C12 andR11 associated with amplifier 308.

In FIG. 13B, integrated circuit 312 is a Rockwell R6522 VersatileInterface Adapter identical to integrated circuit 142 described abovewith reference to FIGS. 8-10. The connections to circuit 312 closelyresemble those to circuit 142. Pins 26-33 of circuit 312 are connectedvia connectors A1-A8 respectively to lines 7-0 respectively of bus 288,and thus indirectly to the computer data bus 284, as explained abovewith reference to FIG. 7. Lines 35-38 of circuit 312 are connected viaconnectors A19-A22 respectively to lines 11-8 respectively of bus 288and thus receive the four least significant bits appearing on thecomputer address bus 286 (see description of FIG. 7 above). Pin 34 ofcircuit 312 receives the RESET signal from line 288-24 via connector AZ,pin 25 of circuit 312 receives the φ2 signal from pin 5 of driver 130B(FIG. 7) via line 288-20 and connector AV and line 22 of circuit 312receives the R/W signal from pin 13 of driver 130A via line 288-21 andconnector AW. Pin 24 of circuit 312 receives the signal DS from pin 4 ofinverter 120A (FIG. 7) via line 290 and connector AF. Pin 23 of circuit312 receives the control signal CSB fro circuit 144A, pin 5 (FIG. 8).Thus, circuit 312 is addressed by the computer by addresses XFEO-XFEF.

The SBLNK/2 signal from pin 10 of circuit 148 (FIG. 8) is fed viaconnectors CT and AB (see description of FIG. 6 above) to pin 1 of 314A.Integrated circuit 314 is a quadruple 2-input positive NAND gate of thecommercially-available 74LS00 type. The second input to pin 2 of gate314A is taken from the +5 V supply line, so that gate 314A acts as aninverter. The output from pin 3 of gate 314A is supplied to pin 16 ofcircuit 312.

As the analog board 280 is presently configured, the only function ofcircuit 312 is to generate the IIG which, as previously explained,causes integration of image intensity by the video camera over a numberof frames. Upon receipt of a preselected address from the computer whichcauses appropriate inputs at pins 23, 24 and 35-38 of circuit 312,circuit 312 loads from the computer data bus 284 (FIG. 7) via lines 7-0of bus 288, a value simultaneously appearing on the data bus andspecifying whether IIG should be high or low. Circuit 312 then proceedsto output the appropriate value of IIG from its pin 2 to connector ANfor transmission to the video camera via driver 130F (see FIG. 6).However, it will be appreciated that circuit 312 has considerable unusedinput/output capacity, and thus provides capability for further digitalinputs/outputs if required in later variations of the interface.

The ACCPIX signal from pin 10 of inverter 120E (FIG. 10) is fed viaconnectors CU and AU to pin 13 of 314B, which is a second NAND gate onthe 74LS00 integrated circuit already mentioned. The second input to pin12 of gate 314B is taken from the +5 V supply line, so that gate 314Bacts as an inverter. The output from pin 4 of gate 314B is fed to pin 10of 314C, which is a third NAND gate on the 74LS00 integrated circuit 314previously mentioned. The second input to pin 9 of gate 314C is takenfrom pin 19 of circuit 312. As the analog board is presently configured,this input to pin 9 of gate 314C is held low, so that 314 simply acts asa second inverter. However, obviously the provision of this connectionto circuit 312 allows for possible gating of ACCPIX by various otherfunctions if such gating is believed to be appropriate for modificationof the image to be shown on the monitor.

Thus, at present, the output from pin 8 of 314C is the original ACCPIXsignal. This signal is passed via a fixed resistor R15 and variableresistor R16 connected in series to pin 2 (the negative input) ofintegrated circuit 316, which is a type CA 3100 analog amplifieridentical to integrated circuit 308 described above with reference toFIG. 13A. The analog video signal from the video camera is fed toconnector AT, which is connected to ground via a resistor R17 and whichis also connected via a capacitor C14, a fixed resistor R18 and avariable resistor R19 also connected in series to pin 2 of integratedcircuit 316.

Circuit 316 receives the conventional power connections, +12 V to pin 7and -12 V to pin 4. Pins 7 and 4 are also connected to ground viaconnectors C15 and C16 respectively. Pins 1 and 8 of circuit 316 arebridged by a capacitor C17 and pin 3 (the positive input) of circuit 316is grounded via a resistor R20. To provide feedback for amplifiercircuit 316, the output from pin 6 of circuit 316 is fed via an RCcircuit (comprising a capacitor C18 and a resistor R21 connected inparallel) to pin 2 of circuit 316. The output from pin 6 of circuit 316is also fed via a resistor R22 to pin 2 (the negative input) of circuit318, which is another type CA 3100 analog amplifier. Pin 3 (the positiveinput) of circuit 318 is grounded via a resistor R23, pins 1 and 8 ofcircuit 318 are interconnected via a capacitor C19, pins 7 and 4 ofcircuit 318 receive the conventional +12 V and -12 V respectively powerinputs. The output from pin 6 of circuit 318 is fed via resistor R24 tothe base of an NPN transistor Q1. A resistor R25 and a capacitor C20 areconnected in series between the +12 V supply line and ground, theresistor R25 being connected to the positive supply line, and themidpoint of the bridge formed by R25 and C20 is connected to thecollector of Q1. The emitter of Q1 is connected to the -12 V supply linevia a resistor R26, to pin 2 of circuit 318 via a resistor R27 and to avideo output line 320 via a resistor R28. To limit the output potentialwhich can be placed on the line 320, line 320 is connected to the anodeof the first of a series of three Zener diodes, D1, D2 and D3 allconnected in series, D3 being connected to ground. The video output line320 is connected via connector AR and line 84 (see description of FIG. 6above). As will be apparent to those skilled in the art, the effect ofthe circuitry shown in the lower part of FIG. 13B is that, when ACCPIXis low indicating a non-accepted pixel, the video output on line 320 issimply an amplified version of the video input from the camera. However,when ACCPIX goes high, the video output in effect reflects ACCPIX (theexact value depending of course upon the value of variable resistorR16), resulting in a heightened intensity on the video monitor. Thus,this circuitry enables an observer to determine visually the acceptedpixels, which will appear with high intensity on the video monitor 72(FIG. 4) and will be recorded by the video tape recorder 74.

FIG. 14A is a timing diagram showing the way in which various signalsgenerated by the controller board are synchronized with signals from thevideo camera. It should be noted that the time-scale in the rowcontroller timing diagram in the upper half of FIG. 14A is differentfrom that in the column controlling timing diagram shown in the bottomhalf of the same figure, although of course, within each timing diagramthe time scale is constant and the various rows of each timing diagramshow the correct temporal correlations of the signals.

The top line in FIG. 14A is the SBLNK signal from the camera. Aspreviously mentioned, this signal is high when video data is beingtransmitted by the camera for the major part of each horizontal line,but goes low for the relatively brief horizontal blanking intervaloccuring between lines. Shown immediately below SBLNK in FIG. 14A isSBLNK/2, the output from pin 10 of flip-flop 148 (FIG. 8). As explainedabove, the interface is designed for use with the camera in theinterlacing mode in which each line of video data is repeated twice andhence, in order to avoid storage of redundant video information by theinterface, it is necessary to ensure that only data from the alternatelines of new video data is acquired by the interface. Flip-flop 148divides the frequency of SBLNK by two, thus producing a signal which ishigh for the first (new) line of each successive pair of lines, and lowfor the second (repeated) line of each pair. Since flip-flop 148 is apositive-edge-triggered flip-flop of the 74LS109 type, both the positiveand negative transitions of SBLNK/2 coincide with the positivetransitions in SBLNK, so that the value of SBLNK/2 during the horizontalblanking intervals remains at the value for the preceding line of videodata. Also because flip-flop 148 is reset by VSYNC (FIG. 8) SBLNK/2 ishigh for the same lines on each frame of video data.

The third line of FIG. 14A shows the end-of-frame signal EOF, the outputfrom in 13 of gate 164A. As explained above, because of the way in whichthe comparators 156-159 operate, EOF goes high at the beginning of thefirst accepted line and goes low at the beginning of the first linefollowing the new line of video data having the last row value latchedin circuit 150. Accordingly, both the positive and negative transitionsof EOF are synchronized with the positive transitions of both SBLNK andSBLNK/2.

The fourth line of FIG. 14A represents the form of the signal ACCROW(the output from pin 11 of gate 164A in FIG. 9) when the row skip valuelatched in circuit 142 is set to 0 i.e. the video computer interface isset to acquire video data from every new line. Basically, ACCROWcomprises EOF gated by both SBLNK and SBLNK/2; this double gating isnecessary to ensure that ACCROW only goes high on new lines of videodata and also that the positive and negative transitions of ACCROW aresynchronized with the corresponding transitions in SBLNK. This doublegating of EOF with SBLNK and SBLNK/2 is effected by NAND gate 167A inFIG. 9. However, because of the presence of the negative-edge triggeredflip-flops 166A and 166B, the beginning and end of the pulses of ACCROWare delayed relative to the beginning and end of EOF. Thus, after thepositive transition of EOF, a complete cycle of SBLNK/2 elapses (i.e.one new line of video data is skipped) before the first positivetransition of ACCROW occurs. Thereafter, with the row skip value set to0, the positive and negative transitions in ACCROW follow thecorresponding transitions in SBLNK for which SBLNK/2 is high until thenegative transition of EOF occurs. Because of the presence of theflip-flop 166A and 166B, a positive transition of ACCROW can occurcoincident with the negative transition in EOF and the simultaneouspositive transitions in SBLNK and SBLNK/2, and a further pulse of ACCROWfollows immediately the negative transition of EOF. Thus, in the exampleshown in FIG. 14A, in which EOF goes high for new rows 3-7 of videodata, ACCROW actually goes high to accept rows 4-8. The remaining twolines of the row controller timing diagram in FIG. 14A show thecorresponding ACCROW signals for the same EOF signal but with row skipvalues of 1 and 2 respectively. Note that the first row accepted is thesame in each case because of the manner in which the counter 162 and thecomparator 172 (FIG. 9) operate.

The re-setting of counter circuits 152 and 154 (FIG. 9) by VSYNC (whichgoes high during the blanking interval successive frames) ensures thatEOF is always generated for the same rows in each frame. Similarly, theresetting of counter circuit 162 by ACCROW ensures propersynchronization of the ACCROW pulses with EOF.

The time controller diagram in the lower part of FIG. 14A illustratesthe temporal correlation between ACCROW and ACCPIX. When ACCROW goeshigh, counter circuits 174 and 175 (FIG. 10) are reset to 0 and countingcan only occur when ACCROW goes low i.e. it is the negative transitionof ACCROW which actually enables circuits 174 and 175 for counting andleads to the generation of ACCPIX. Furthermore, since pin 3 of circuits174 and 175 is held high, it will be seen from the truth table for the74LS93 counter that counting will only occur when ERC, the input to pin2 of each circuit goes low; this ensures that positive transitions insignal 164-1 are synchronized with positive transitions in ERC, whichindicate the start of new pixels (the signal ERC from the video camerais arranged so that it is the negative transitions in this signal, andthus the positive transitions in the inverse signal ERC, which indicatethe start of new pixels.)

FIG. 14A shows a specimen signal 164-1 in which columns 2-5 areaccepted. This is purely for illustrative purposes; as those skilled inthe art will appreciate, since the negative transition of ACCROWcoincides with a negative transition in SBLNK, the period immediatelyfollowing the negative transition in ACCROW is actually horizontalblanking interval for which no meaningful video data are received.

The next line below signal 164-1 in FIG. 14A is the ACCPIX signalcorresponding to the 164-1 signal shown and with the column skip valueset to 0. For reasons exactly parallel to those discussed above withreference to EOF and ACCROW, the presence of the flip-flops 173A and173B (FIG. 10) delays both the positive and negative transitions in thisACCPIX signal by one complete cycle of ERC (i.e. by one full pixel)relative to the corresponding transitions in 164-1. Unlike ACCROW, whenthe column skip value is set to 0, ACCPIX remains high for the fullwidth of the window because there are no blanking intervals betweenadjacent pixels comparable to the horizontal blanking interval betweenadjacent lines reflected in the low portions of SBLNK. It is believedthat those skilled in the art will have no difficulty in understandingthe generation of the ACCPIX signals shown for column skip values of 1and 2 respectively, since their method of derivation should be obviousfrom the foregoing discussion of ACCROW. Again, note that whatever thecolumn skip value, the first accepted pixel is always the same.

FIG. 14B is a timing diagram showing the temporal correlation of varioussignals produced on the memory board shown in FIGS. 11 and 12. Theuppermost line in FIG. 14B is the COM/CAM signal on line 304. As alreadyexplained, this signal goes low, as shown on the left-hand side of FIG.14B when the computer instructs the camer to acquire video data. Thenext line of FIG. 14B shows the signal ERC previously discussed withreference to FIG. 14A. The third line of FIG. 14B shows the ACCPIXsignal previously shown in the fourth line of the column controllertiming diagram in FIG. 14A; for simplicity, in the following discussiona column skip value of 0 is assumed.

The fourth line of FIG. 14B shows the intervals at which the address tobe used by the memory can change, and the subsequent line shows thecorrespondingly synchronized intervals at which the data on the bus 306can change. Both the address and the data signals are coursesynchronized with each other and with ERC, since ERC undergoes acomplete cycle for each pixel while the address and data signals changeonly between adjacent pixels.

The sixth line of FIG. 14D represents the output from pin 9 of circuit196 (FIG. 11). Since this represents the least significant bit of the12-bit address generated by counters 186, 188 and 190 when COM/CAM islow, signal 196-9 is low and high in alternate pixels when ACCPIX ishigh (since counters 186, 188 and 190 can only be enabled when ACCPIX ishigh, because of the presence of gate 198A). When ACCPIX is low, signal196-9 remains low.

The next two lines of FIG. 14B represent the latch-odd and latch-evensignals on lines 213 and 217 respectively. When these two signals arebeing produced with COM/CAM low, they are always of opposite sign. Theduration of the pulses in these two signals is the same as 196-9, butbecause of the presence of the flip-flops 208A and 208B (FIG. 11) thenegative transitions of the latch-odd signal is one-half pixel, and thenegative transition of the latch-even signal 11/2 pixels, behind thefirst positive transition of signal 196-9. Similar delays occur at theend of the last negative transition of signal 196-9.

The last four lines of FIG. 14B show the four memory enable signals onlines 1-4 respectively of bus 219 (FIGS. 11 and 12). As will readily beapparent to those skilled in the art, these memory enable signals areproduced by combining the latch-odd and latch-even signals with thesignals from pins 10 and 11 of circuits 214 and 220, which represent thesecond least significant bit of the 12-bit address generated by countercircuits 186, 188 and 190 and relayed by multiplexer circuit 192, 194and 196. Thus, for example, memory enable 1 only goes low on the first,third etc. low values of latch-odd, while memory enable 3 only goes lowon the second, fourth, etc. low value of latch-odd. The relationshipbetween latch-even and memory enables 2 and 4 is exactly the same.

To understand lines 9-12 of FIG. 14B, it is necessary to refer back toFIG. 12, and in particular the connections to the camera buffers 224 and232. For convenience, in the following description, successive pixelperiods will be designated by the numbers shown on the line designated"196-9" in FIG. 14B.

As previously mentioned in connection with FIG. 12, pin 1 (the outputenable of circuits 224 and 232 receives the COM/CAM signal, which iskept low when the computer instructs the interface to acquire videodata. Accordingly, when the interface is acquiring video data, circuits224 and 232 always produce outputs. Because the video data arriving onbus 306 vary in an unpredictable manner, it is not possible to determinein advance whether the value on any line of bus 306 will change betweenany two adjacent pixels. However, it is known that such changes on bus306 will only occur at transitions between adjacent pixels. Accordingly,when ACCPIX in FIG. 14B goes high between the pixels designated 0 and 1,the new values present on bus 306 will be reflected substantiallyimmediately in the outputs from both circuits 224 and 232, since at thistime both the LATCH-odd signal on line 213 and the LATCH-EVEN signal online 217 are both high at this time, permitting the inputs of buffers224 and 232 respectively to change substantially instantaneously withany change in the inputs thereto. However, half way through pixel 1, theLATCH-ODD signal goes low, thereby latching the outputs of circuit 224at their existing value i.e. at the values corresponding to the videodata for pixel 1. Accordingly, the outputs from buffer 224 will notchange when the video data change between pixel 1 and pixel 2, and thevideo data for pixel 1, which appeared on the outputs of circuit 224 atthe beginning of pixel 1, will remain fixed until half way through pixel2, when the LATCH-ODD signal again goes high. Thus, the video data forpixel 1 remain on the outputs of buffer 224 for one and one-half pixelperiods, as indicated in the line designated "224-TIMING" in FIG. 14B,in which the blank areas denote the periods in which the outputs ofbuffer 224 cannot change and the shaded areas indicate the periodswithin which they can change. Since the LATCH-ODD signal only goes lowin alternate pixels, the effect is that the video data for eachodd-numbered pixel are present on the outputs of buffer 224 for one andone-half pixel periods. For example, the line designated "224-SAMPLE"shows the value of any output of 224 for which the corresponding inputis a 0 at pixels 1 and 5 and 1 at pixel 3.

The operation of buffer 232 is exactly similar except that, of course,since the negative and positive transitions of LATCH-EVEN are 1 fullpixel period behind the corresponding transitions in LATCH-ODD, it isthe video data for the second, fourth and sixth etc. Accepted pixels arepresent on the outputs of circuit 232 for one and one-half pixelperiods, as indicated by the line designated "232-TIMING" in FIG. 14B.The line designated "232-SAMPLE" shows the value of any one output ofcircuit 232 for which the corresponding input is a 1 at pixels 2 and 6and a 0 at pixel 4.

WELD POOL WIDTH MEASUREMENT PROGRAM

The program used in the process control computer 80 shown in FIG. 4 tomeasure weld pool width in the image observed by the camera 68 (FIG. 4)will now be described with reference to FIGS. 15, 16A, 16B, 17 and17A-H.

FIG. 16A depicts an idealized version of the image seen by the camera 68of a weld puddle and the surrounding metal. The image shows severaldifferent zones, namely base metal 350, which surrounds the weld pooland reflects light only diffusely, molten metal 352, which comprises theweld pool itself and which reflects light in a mirror-like fashionbecause of its molten state, and resolidifying metal 354 lyingimmediately adjacent the edge of the weld pool and in which the moltenmetal has begun to resolidfy. Also shown in FIG. 16A is the electrode"shadow" 356 which, for reasons described above, is present in theinstant axial viewing apparatus. (It will of course be appreciated thatthe so-called "shadow" is an artifact of the viewing system and that theelectrode does not in fact throw a shadow on the weld pool. However,hereinafter the term "shadow" will be used for convenience.) Forsimplicity, in FIG. 16A the shadow 356 has been shown as locatedcentrally in the weld pool, although in actual operation it has beenfound that the electrode shadow will appear in various locations in thecentral area of the weld pool but not necessarily in the center thereof.Line 358 is one of the scanning lines of the camera 68 (FIG. 4) whichproduces the image shown in FIG. 16A, and FIG. 16B shows an idealizedgraph of light intensity along the line 358. It will be seen from FIG.16B that five separate zones of light intensity are present along theline 358. Firstly, since line 358 passes through the electrode shadow,it includes a central zone 360 of low light intensity caused by theelectrode shadow 356. On either side of the zone 360 are two zones 362caused by the molten weld pool 352. Finally, the resolidifying metal 354produces outer zones 364 and 366 of relatively low light intensity.Beyond the zones 364 and 366, the light intensity tends downwardly asthe intensity of reflection from the metal 350 diminishes.

As shown in FIG. 16B, it has been found that two local minima of lightintensity are present at the junctions between zones 362, 364 and 366;these local intensity minima occur at the edges of the weld pool andthus to measure the weld pool width it is necessary to detect theselocal minima and to calculate the distance between them. Obviously, thetrue weld pool width will only be determined if the line 358 extendsacross a diameter of the weld pool. However, when using the instantaxial viewing apparatus the weld pool will always be located in the samearea of the image and thus even if the line 358 does not lie on adiameter of the weld pool, measuring the distance between the localminima of light intensity on the line 358 will still yield a valuerepresentative of weld pool width, which will be sufficient, if, forexample, it is only intended to use the data for maintaining weld poolwidth constant. The program described below analyzes only a single lineof video data, allowing the operator to select which line is to beanalyzed and thus to position the line 358 on a diameter of the weldpool in order to produce a proper weld pool width. It will be apparentto those skilled in the art, that by routine modification of the programdescribed below, a series of lines of video data from the same imagecould be analyzed and the greatest width of weld pool thus determinedcalculated so as to yield a true maximum weld pool width without manualsetting of the apparatus to position the line 358 in the correctposition.

In the presently preferred embodiment of the invention, the computer 80(FIG. 4) is a Rockwell AIM-65 computer which uses the Rockwell 6502microprocessor chip. The AIM-65 computer, which is manufactured byRockwell International Corporation, is used in the stock configurationas received from the manufacturer, with the jumpers in the standardconfiguration shown in the manufacturer's operating manual. The programdescribed below was written in the 6502 microprocessor chip assemblerlanguage, further details of which are in the 6502 reference manual. Allthe programs described below written in this assembler language can beaccommodated on a type 2716 EPROM inserted into socket Z-26 of theexpansion board of the AIM-65 computer. As previously described, thecomputer operates on video data stored in the memory board of the videocomputer interface.

The program shown in FIGS. 15 and 17-17H is, as previously mentioned,intended to find the position of the local minima of intensity denotingthe edges of the weld pool by analysis of a single line of video data,such as the line 358 in FIG. 16A. Accordingly, to use this program, theoperator sets the video computer interface so that the window from whichvideo is stored comprises a single complete line of video data. This isaccomplished by setting the last row parameter equal to the first rowparameter plus one, the first column value to 0, the last column valueto FF(255 in decimal notation) and the row skip and column skip valuesboth to 0. The resulant-single line window appears in the highlightedpicture seen on the video monitor 72 (FIG. 4) as a single white lineclosely resembling a typical cursor and accordingly this single-linewindow may hereinafter be referred to by the term "cursor".

The program assumes that the light intensity curve along the line to beanalyzed has the form shown in FIG. 16B, and that pixel 127 (75 inhexadecimal notation) lies within zone 360 in the light intensityminimum caused by the shadow of the electrode. Thus, the program willonly function correctly if the operator sets the cursor so that the line358 does indeed pass through the shadow of the electrode so that thezone 360 is present in the path of light intensity. Furthermore, theprogram assumes that the light intensity maxima present at the junctionsbetween zones 360 and 362 are sufficiently bright that the correspondinglight intensity values will have to be reduced to the predeterminedlimit by the subroutine MEAN described below, but that the areas whichinclude the local intensity minima i.e. the outer parts of zones 362 andzones 364 and 366, are of sufficiently low intensity not to be set tothis predetermined limit by subroutine MEAN. Finally, the programassumes that any aberrations in light intensity values within zones 362are insufficient to produce false local minima after the light intensitydata has been smoothed by the various techniques described below. It hasbeen found that the foregoing conditions are normally satisfied inpractice.

In FIGS. 17-17H, the prefix "#" denotes an absolute number rather than avariable or register name. Prefix "$" denotes a hexadecimal value.

The overall architecture of the program employed is shown in FIG. 15. Aswill be seen from that figure, the program comprises a MAIN program andan INTERRUPT program. The MAIN program begins at 400 and proceeds to ablock 402 where the computer is initialized and various parameters areacquired. The parameters acquired specify the window from which thememory board of the video computer interface is to acquire video dataand include the first and last line and column of the window and the rowskip and column skip functions which specify for exactly which pixels ofvideo data should be stored by the video computer interface. Theappropriate parameters are entered upon the keyboard of the computer 80and stored in appropriate places therein, in a manner conventional inthe art. After the appropriate parameters have been acquired at block402, the program proceeds at 404 to start the video data analysis cycleby commanding the video computer interface to acquire the specifiedvideo data. Next, the waits at block 406 until new video data isavailable (from the INTERRUPT program). As will be explained below, whennew data is available, the INTERRUPT program sets a new data flag,MEMFL, and the MAIN program waits at block 406 until it detects thatthis flag has been set. When setting of this flag is detected, the MAINprogram proceeds, at block 408, to clear the flag MEMFL and then, atblock 410, passes through a display data routine which outputs data tothe oscilloscope 76 (FIG. 4) for observation by the operator. Obviously,if the oscilloscope display of data is not required, block 410 can beeliminated. From block 410, the MAIN program proceeds at block 450, toexecute program PWDTHX to calculate the weld pool width from thenewly-acquired data. Once PWDTHX has been completed, the MAIN programproceeds to decision block 412, which instructs the video computerinterface to acquire the appropriate portion of another frame of videodata. The MAIN program may leave block 412 to a termination point 414 ifno data is to be accepted, but normally loops back from block 412 toblock 416 to await the new data. Thus, the MAIN program operates as acontinuous loop only directing the video computer interface to acceptnew data (at block 412) when the data processing program PWDTHX hasprocessed the previous data (at block 450).

The interrupt routine, IRQ, is triggered by receipt of an interruptsignal by the computer from the video computer interface via the line420 (FIG. 5). The interrupt program begins at 420' (FIG. 15) andproceeds to a three-way decision block 422 which determines which typeof interrupt is occuring.

The first possible type of interrupt is designated VSYNC COUNTER. TheVSYNC COUNTER interrupt is produced by a counter (located within thecomputer) which counts VSYNC interrupts received from the video cameravia the video computer interface, thereby counting the number of framesof data which have elapsed. The computer can be set by the operator sothat every fourth, fifth or similar frame of video data will be acquiredby the video computer interface. In this setting of the program a VSYNCCOUNTER interrupt will be generated after the appropriate number offrames has elapsed and the program will proceed from block 422 via adecision 424 (whose purpose will be explained below) to a block 430,which causes the appropriate parameters (those acquired at block 402 ofthe main program) to be sent to the video computer interface. Next, atblock 432, the video computer interface is set to acquire a frame ofvideo data i.e. to store the video data corresponding to the selectedpixels in the memories on the memory board of the video computerinterface. This is effected simply by instructing circuit 142A (FIG. 8)to set COM/CAM low. Finally, at block 434 the VSYNC COUNTER is reset to0 and the interrupt program terminates at 438 with a return to the mainprogram.

Although the interrupt program functions in the manner described abovewhen it is only required to acquire a single, unintegrated frame ofvideo data. The interrupt program is also provided with means to takeadvantage of the integration feature of the preferred TM2500 videocamera. As already mentioned, if the IIG is turned on (i.e. the signalIIG set to a low level) the camera will integrate over a number offrames. This integration feature allows an operator to bring the pixelgrey intensity within the optimum range for analysis. For example, thesystem might be operated so that only every 10th frame of video datawill be stored in the video computer interface but the intensity of theframe that is stored will be integrated over three "normal" frames. Inthis situation, a VSYNC COUNTER is initially set to 7 so that when sevenframes of video data have passed the interrupt program leaves block 422and enters block 424. At block 424, the program determines (fromregisters representing previous manual settings on the keyboard) thatthe IIG signal should be turned on and therefore leaves block 424 viathe YES exit thereof to block 426, where it determines whether the IIGsignal is in fact on. On the first pass through block 426, the signalwill of course not be on, so the program proceeds from block 426 toblock 428, where the computer causes the video computer interface toturn the IIG signal on and resets the VSYNC COUNTER to an appropriatevalue. If, as in the example suggested above, integration is to beeffected over three frames, block 428 will set the VSYNC counter to thevalue three. From block 428, the program proceeds to block 436, which isexactly similar to block 430 and causes the computer to send dataspecifying the appropriate pixels to be accepted to the video computerinterface. However, since no block corresponding to block 432 followsblock 436, the effect of block 436 is only to cause highlighting of theappropriate pixels on the video monitor. From block 436, the interruptprogram returns to the main program via 438.

Thus, when the computer is operating in a mode which requiresintegration of the image by the camera, the first pass through block 244causes the IIG signal to be turned on and the counter to be reset tospecify the number of frames to be integrated, but does not cause thevideo computer interface to be set to acquire data, since the programnever passes through block 432. After the appropriate number of framesfor integration, the VSYNC COUNTER flag will again be set and the block424 entered a second time. The program will again proceed to block 426,but on this occasion, since the IIG signal is already turned on, it willproceed from the YES exit of block 426 to block 430 and proceedsuccessively through block 432 and 434 as previously described to causethe video computer interface to acquire data. At block 434, not onlywill the counter be rset to the appropriate value (7 in the aboveexample), but the IIG signal will be turned off. Finally, the interruptprogram will return to the main program via 438.

The second possible type of interrupt flag is a VSYNC flag, which simplyindicates receipt of a VSYNC signal from the camera by the videocomputer interface. (As may be seen from the description of thevideo-computer interface, the only interrupt signal actually sent to theinterface to the computer is signal IRQ on line 420. Upon receipt of anIRQ signal, the computer interrogates a register within circuit 142(FIGS. 8-10), to discover whether the IRQ signal was caused by a VSYNCsignal or an EOF signal, since circuit 142 generates an IRQ signal onreceipt of either VSYNC or EOF.) When, at block 422, a VSYNC flag isfound, the program proceeds directly to the aforementioned block 436 atwhich the proper parameters are sent to the video computer interface inorder to cause highlighting of the display on the video monitor and ofthe interrupt routine then exits at 438.

The third type of interrupt handled by the interrupt program is anend-of-frame (EOF) interrupt. When a EOF interrupt is detected at block422 (indicating that EOF has gone low after the last selected row hasbeen passed), the program proceeds from block 422 to a block 440 whichtests whether video data has been accepted. In fact, the decision block440 merely tests whether the COM/CAM signal is low, indicating that (atblock 432) the video computer interface was set to accept video data. Ifat block 440 it is determined that video data has been accepted, theprogram proceeds, at 442, to set the new data flag MEMFL, which, asexplained above, causes the main program to process the new data. Fromeither the NO exit of block 440 or from block 442, the program proceedsat 444 to check for keyboard input, by checking the keyboard buffer, andto effect appropriate adjustment of parameters. Those familiar with theAIM-65 computer will be aware that it contains a buffer which can storeonly the latest keystroke by the operator. However, since the interruptprogram will proceed through block 444 once each frame (thus typically30 times a second), handling a single keystroke at each pass throughblock 444 is sufficient. The system is arranged so that the operatorcan, by means of single keystrokes move the first row of the "window" tobe analyzed up or down, move the last row up or down and move the firstand last columns left or right. To move any of these parameters morethan one line or pixel at a time, repeated keystrokes are required.Further, single keystrokes will effect modification of the row skippingand column skipping functions. Since this manner of modifying parametervalues within a computer program is conventional in the art, it isbelieved that no further explanation is required. From block 444, theinterrupt program, as usual, returns to the main program via 5483.

Those skilled in the art will appreciate that the provision of thethree-way decision block 422 is optional and that if desired theinterrupt routine shown in FIG. 15 could be replaced by three separateinterrupt routines.

Further details of the data processing routine PWDTHX are shown in FIG.17. From that figure it will be seen that the first step in PDWTHX is ablock 452 at which registers X and Y are intialized. Next, at block 460,the X register is incremented and a subroutine MEAN is run to produce anaverage value of the intensity at the point X. Next, at 468, the programtests whether all the points of video data have been processed i.e.whether X has reached its maximum value. If not, the program loops backto 460 and continues cycling through this loop until all points havebeen processed. Once all points have been process, the program leavesblock 468 via the positive exit thereof and proceeds, at 469, to runsuccessively subroutines CLEAN, TRANSF, SMOOTH, TRANSF and SLOPE.Subroutine CLEAN looks for (erroneous) negative numbers in the videodata, sub-routine TRANSF transfers data between tables, sub-routineSMOOTH removes abberational points which do not conform to the type ofcurve expected (as shown in FIG. 16B) and finally sub-routine SLOPEdetects the local minima denoting the edge of the weld pool and hencethe width of the weld pool.

After all the subroutines in block 469 have been completed, the routinePDWTHX proceeds, at 650, to output data generated at block 469 to theoscilloscope (FIG. 4). Next, at 652, the width value generated at block469, which has been stored in a register $WIDTH, is transferred to a"new width" register $NWDTH. Then, at block 654, a differential width iscalculated by substracting $NWDTH from a previously stored "old width"$OWDTH. Also at 654, the old width value $OWDTH is replaced by the newwidth value $NWDTH, in order that the width just calculated can serve asthe old width value for the next pass through block 654. The programthen proceeds, at block 656, to output the differential width justcalculated to the robot control device, which will be described indetail below with reference to FIG. 18.

As already mentioned, the main and interrupt programs shown in FIG. 15are programmed onto a type 2716 EPROM inserted in socket Z-26 in theexpansion board of the Rockwell AIM-65 computer. However, because ofspace limitations, the various subroutines shown in FIG. 17 are loadedinto a similar EPROM placed in socket Z-25 on the same board.

Details of the sub-routine MEAN are shown in FIG. 17A. This program sumsthe intensity values for each particular point with the similar valuesfor the 3 points on each side, to establish a MEAN value of intensity ateach data point. As those skilled in the art will appreciate, thisaveraging process removes system noise and allows the analysis to usemore reliable data. Also, sub-routine MEAN sets an upper limit on theaveraged intensity values which will be handled by the latersubroutines. Since the program is only determining weld pool width, theregions of very high intensity in the central parts of the zones 362(FIG. 16B) are of no interest and setting an upper limit on theintensities being processed in later subroutines helps to avoidgenerating spurious values caused by abbreviations in the weld pool.

Subroutine MEAN begins, at 461, by saving the value of X (previously setat block 460 in FIG. 17) to a storage register $TEMX. The X register isthen set equal to X-3 and registers Y and $TOTAL are set to 0. Next, at462, the data value $DATA, X, representing the intensity at point X isadded to $TOTAL and, at 463, the resultant value of $TOTAL is checked tosee if it is less than a predetermined limiting value 7F. (The question"$TOTAL(+ve)?" at block 463 actually means "Is the most significant bitof the eight-bit number a 0?". As those familiar with the RockwellAIM-65 computer will be aware, the 6502 microprocessor is an eight-bitmicroprocessor and, of course when this microprocessor is in facthandling eight-bit numbers which require a sign, the most significantbit of the 8-bit number is used as the sign bit. Although the lightintensity data never involves negative numbers, it is convenient to usethe fine-testing operation of the 6502 microprocessor to test when therunning total in $TOTAL exceeds 127 (in decimal notation).) Normally,$TOTAL would be less than 7F and the sub-routine will therefore proceedfrom 463 to 465, where the registers X and Y are incremented and then to466 where Y is tested to see if it is equal to 7. Since Y has been setto 0 at 461, on the first six passes through blocks 465 and 466 Y willnot be equal to 7 and thus the subroutine will leave block 466 via theNO exit thereof and loop back to block 462. However, after the seventhpass through blocks 462, 463 and 465, $TOTAL will be equal to the sum ofthe values of $DATA, X for the point X and the three points on eitherside, and Y will be incremented to 7 at 465. Accordingly, on thisseventh pass the subroutine will leave block 466 via the YES exitthereof and proceed to block 467, where the "correct" value of X isreturned from $TEMX to the X register and the value of $TOTAL is storedin a table of values, TABLE, X. From block 467, the subroutine returnsto the program PWDTHX at 468.

If, on any pass through the block 463, it is determined that $TOTAL isnot less than 7F, the sub-routine proceeds, at 464, to set $TOTAL equalto 7F, and then proceeds through blocks 467 and 468 as previouslydescribed. Thus, the value of $TOTAL recorded in TABLE X at 467 cannever exceed 7F.

As previously mentioned and as indicated at block 468 in FIG. 17,subroutine MEAN is repeated for each point in the line of video dataacquired. Once this has been done, the next subroutine to be applied issubroutine CLEAN (shown in FIG. 17H), as indicated by block 469 in FIG.17.

As shown in FIG. 17H, from a start point at block 580, subroutine CLEANproceeds, at block 582, to set X equal to FF (255 in decimal notation)and then, at block 584, to test whether the corresponding lightintensity value placed in TABLE, X by subroutine MEAN is negative i.e.whether it is greater than (decimal) 127. If so, the value in TABLE, Xis replaced by FF at block 586. From block 586, or from the negativeexit of block 584, the program proceeds at block 588, to decrement X andthen to test, at block 590, whether X is equal to 0. If not, the programloops back to block 584 but if X is equal to 0, the subroutine is exitedvia block 592.

It will be apparent to those skilled in the art that the sole effect ofsubroutine CLEAN is to replace any averaged light intensity values inTABLE, X which are greater than $75 with $FF. Subroutine CLEAN wasoriginally designed to deal with the first three and last three pixelsof video data which, as will be apparent to those skilled in the art,cannot be processed by subroutine MEAN because the combined effect ofblocks 461, 465 and 466 in subroutine MEAN (FIG. 18A) is that thissubroutine can only operate on values of X such that values are presentin TABLE, X for values from X-3 to X+3. (Although not shown in FIG. 17A,for obvious reasons subroutine MEAN must incorporate screeningoperations to ensure that it does not attempt to process values of X forwhich not all of the necessary values are present in TABLE, X.) It hasnow been realized that subroutine CLEAN is in fact unnecessary since,except for the first three and last three values of X, no numbersgreater than $75 can remain in TABLE X because of the presence of blocks463 and 464 in subroutine MEAN. Furthermore, even the first three andlast three values in TABLE, X, which might contain values notcorresponding to averaged video data from subroutine MEAN, in no wayaffect the determination of weld pool width since, as will be describedbelow, subroutine SLOPE determines weld pool width by beginning from themiddle of the line of video data and working outwards in bothdirections, ceasing inspection of the light intensity data when theminima are located. Accordingly, any aberrant values representing videodata at the extreme ends of the line, these being the values in TABLE, Xwhich are not processed by subroutine MEAN, will not be reached.Accordingly, if desired subroutine CLEAN and the subsequent execution ofTRANSF in block 469 of subroutine PWDTHX (FIG. 17) may be omitted tosave computer time, which is of course always desirable when thecomputer is being used to control weld pool width in real time.

As shown in block 469 of program PWDTHX in FIG. 17, following theexecution of CLEAN, the next subroutine to be executed is TRANSF shownin FIG. 17G. From a start point at block 570, subroutine TRANSFproceeds, at block 572, to load $FF into register X. Then, at block 574,the corresponding averaged light intensity data from TABLE, X aretransferred to DATA, X the corresponding location in a second tableDATA. X is then decremented and tested at block 576 to determine if ithas been reduced to 0. If not, the program loops back to block 574;however, when X has been reduced to 0, the subroutine TRANSF is exitedvia block 578.

As will be apparent to those skilled in the art, subroutine TRANSFsimply serves to transfer all data from TABLE to DATA. The purpose ofthis transfer is simply to save memory space and to avoid having toprovide such space for several different tables containing the severaldifferent sets of data generated during processing of each line of videodata. As will be apparent from FIG. 17, subroutines MEAN, CLEAN, SMOOTHand SLOPE operate sequentially on any given set of video data so thatthe starting data for each subroutine can be discarded as the subroutinehas been completed.

As shown at block 469 in FIG. 17, following this first execution ofsubroutine TRANSF, the next subroutine to be executed is SMOOTH shown inFIG. 17E. The purpose of subroutine SMOOTH is simply to execute SMTH forall values of X from $FE to $01. As shown in FIG. 17E, subroutine SMOOTHaccomplishes this by proceeding from a start point at block 520 to block527, where X is set equal to $FE. Next, at block 524, subroutine SMTH isrun and X is decremented, then at block 526 X is tested to see if it isequal to 0. If not, the program loops back to program 524, but when X isequal to 0 subroutine SMOOTH is exited via FIG. 17E.

Subroutine SMTH shown in FIG. 17F effects a final smoothing of the videodata in order to eliminate local aberrations in the data which generatefalse local minima. As may be seen from a simple sketch, if a series ofpoints are located on a relatively smooth curve, except that one of thepoints is, because of some random error, so displaced from the smoothcurve that it is greater than or less than both of the adjacent points,a local minimum and local maximum will always be present in the curve inthe area of the erroneous point, the erroneous point itself being eitherthe maximum or minimum depending upon whether it is above or belowrespectively the smooth curve through the remaining points, and one ofthe points adjacent the erroneous point constituting the complementaryminimum or maximum. To deal with such erroneous points, subroutine SMTHtests each value in DATA, X and, if the value is found to be greaterthan or less than both the adjacent values, replaces it with the mean ofthe adjacent values. As may also be seen from a simple sketch, if thesame operation is performed on points representing a true maximum ortrue minimum in which the maximum or minimum is greater than or lessthan all of at least the four points closest thereto, the most that canhappen to the curve is that the position of the maximum or minimum isshifted by one point in either direction. In practice, the risk ofapparent displacement of the true minima by a single point (i.e. asingle pixel) is negligible and much outweighed by the lowering of therisk of finding a completely erroneous minimum. Moreover, in practicesubroutine SMTH will often not change the location of the true minima atall since minima tend to be represented by several pixels ofsubstantially the same light intensity, a formation on which SMTH willhave no effect.

As shown in FIG. 17F, subroutine SMTH proceeds from a start point atblock 540 to a block 542, where DATA, (X-1) is transferred to a registerLOC1; DATA, X is transferred to a register MARK; and DATA, (X+1) istransferred to a register LOC2. Next, at block 544, the program testswhether the values in LOC1 and LOC2 are equal. If they are, the programproceeds to a block 544, where it tests whether MARK is equal to LOC1.If so, both the point being tested (DATA,X) and the two adjacent pointsall have the same value and no action is required other thantransferring DATA,X to TABLE,X so subroutine SMTH places its results inTABLE,X. Accordingly, if block 554 yields a positive result, DATA,X istransferred to accumulator register ACCUM at block 562 and then at block564, the contents of ACCUM are transferred to TABLE,X and subroutineSMTH is finally exited via block 566. If, however, block 554 yields anegative result, MARK is either greater than or less than both LOC1 andLOC2, so that DATA,X is deemed to be an erroneous point. Accordingly, inthese circumstances the program proceeds from the negative exit of block554 to a block 560 where ACCUM is set equal to (LOC1+LOC2)/2, and thenthis averaged value in ACCUM is transferred to TABLE,X at block 564 andsubroutine SMTH exited at block 566 as previously described.

If at block 554 it is found that LOC1 and LOC2 are not equal, theprogram proceeds to block 566, where it tests whether MARK is equal toLOC1. If so, point DATA,X is equal to one of its adjacent points, istherefore deemed not to be an erroneous point and accordingly, thesubroutine proceeds through blocks 562, 564 and 566 as previouslydescribed. If, however, at block 546 it is found that MARK is not equalto LOC1, the program proceeds to block 548 and tests whether MARK isequal to LOC2. If so, the value of DATA,X is again equal to one of theadjacent points and is deemed not to be an erroneous point, andaccordingly the program proceeds through blocks 562, 564 and 566 aspreviously described.

If block 548 yields a negative result, none of the values in MARK, LOC1and LOC2 are equal. Accordingly, the program proceeds to block 550 andtests whether LOC1 is greater than LOC2; if so, LOC1 and LOC2 areinterchanged at block 552. From either the positive exit of block 550 orfrom block 552 the program proceeds to block 556. Blocks 550 and 552 arenecessary because, as may be seen from FIG. 16B, the light intensitycurve has a positive gradient in one zone 362 and a negative gradient inthe other. Accordingly, to make the remaining operations of subroutineSMTH work correctly, it is necessary to ensure that LOC1 is greater thanLOC2.

At block 556, the program tests whether MARK is greater than LOC1. Ifso, MARK is greater than both LOC1 and LOC2, DATA,X is deemed to be anerroneous point and the program proceeds through blocks 560, 564 and 566as previously described, thereby ensuring that the value placed inTABLE,X is not DATA,X but is instead the mean of DATA,(X-1) andDATA,(X+1). If block 556 yields a negative result, the program proceedsto block 558 where it tests whether MARK is greater than LOC2. If not,MARK is less than both LOC1 and LOC2, DATA,X is deemed to be anerroneous point and the program proceeds through blocks 560, 561, 566 aspreviously described. If, however, block 558 yields a positive result,DATA,X is intermediate the adjacent points, is deemed not to be anerroneous point and accordingly, the program proceeds through via blocks562, 564 and 566 as previously described, thereby placing the true valueof DATA,X in TABLE,X.

Subroutines SMOOTH and SMTH complete the smoothing of the video data.Following execution of SMOOTH, as indicated at block 469 in FIG. 17,subroutine TRANSF is again executed to transfer the fully smoothed dataplaced in TABLE by subroutine SMTH to DATA. The program is now ready tofind the local minima denoting the weld pool edges, this operation beingaccomplished by subroutine SLOPE shown in FIG. 17B.

As shown in FIG. 17B, subroutine SLOPE proceeds from a start point atblock 470 to block 471 where it sets a direction indicator flag M equalto 0. Flag M is necessary because, for reasons previously described,subroutine SLOPE finds the two local minima associated with the weldpool edges by working outwardly from the "well" in light intensity inzone 360 (FIG. 16B). Flag M serves to indicate which way subroutineSLOPE is scanning light intensity data, M=0 indicating a scan to theleft and M=1 indicating a scan to the right (in FIG. 16B).

From block 471, subroutine SLOPE proceeds to block 472 where X is setequal to $75 (117 in decimal notation). Since the TN2500 camera hasabout 235 usable pixels on each horizontal line (the remaining pixelsbeing occupied by the horizontal blanking interval), pixel 117 will besubstantially in the middle of the line and hence within zone 360 inFIG. 16B. Naturally, if for any reason an apparatus is used in which theimage of the weld puddle is not exactly centered in the TV screen, itmay be necessary to adjust the value of X loaded at block 472. Next, atblock 473, subroutine EVALP is executed. Since subroutine EVALP is verysimple in both concept and execution it will be described at this point.

As shown in FIG. 17D, subroutine EVALP proceeds from a start point atblock 510 to a block 512, where M is tested to see if it is equal tozero. If so, M is decremented at block 514; if not, X is incremented atblock 518. From block 514 or 518 subroutine EVALP is exited from block516 back to subroutine SLOPE. Thus, subroutine EVALP decrements X when Mis 0 and increments X when X is equal to 1, thereby moving one pixel tothe left or right according to the value of M.

Thus, on each pass through subroutine SLOPE, since M is initially setequal to zero at block 471, block 473 merely serves to decrement X. Fromblock 473, the program proceeds, at block 474, to test whether DATA,Xthe fully smoothed light intensity value for pixel X provided bysubroutines SMTH and TRANSF, is equal to $75. So long as the value of Xis such that the corresponding pixel lies within zone 360 in FIG. 16B,DATA,X will be less than $75 and accordingly the program will loop backfrom block 474 to 473. However, after a number of passes through blocks473 and 474, X will have been decremented sufficiently that theleft-hand edge of zone 360 in FIG. 16B will have been reached. At thispoint, the values in DATA increase from their relatively low values to$7F since, as explained above, the maxima at the junctions of zones 360and 362 in FIG. 16B are of sufficiently great intensity that, duringexecution of subroutine MEAN shown in FIG. 17A, the running total in$TOTAL will eventually become greater than $7F and subroutine MEAN willproceed to place $7F in each of the appropriate locations in TABLE.Accordingly, when subroutine SLOPE reaches the data relating to theinner parts of zone 362 in FIG. 16B, block 474 will produce a positiveresult and the program will proceed to block 474 where routine EVALP isagain executed, thereby decrementing X.

From block 475 the program proceeds to block 476 which is identical toblock 476. On the first few passes through blocks 475 and 476, the lightintensity values in DATA still relate to the "saturated" regionsadjacent the maxima of the light intensity curve for which the values inDATA are $7F, operation 476 will produce a positive result and theprogram will loop back to block 475. However, as the value of X isdecremented by successive passes through block 475, eventually thevalues from DATA tested at block 476 will relate to non-saturatedregions in the outer part of zone 362, and at this point block 476produces a negative result, causing the program to proceed to block 477.

At block 477 subroutine EVALP is then executed to further decrement X.Next, at block 478, M is tested to see if it is equal to zero. When thesubroutine SLOPE first reaches block 478, M will be equal to zero havingbeen so set at block 471, and the program will therefore proceed toblock 481 where subroutine SLP shown in FIG. 17C is executed. Sincesubroutine SLP is very simple, it is convenient to describe it at thispoint.

As shown in FIG. 17C, subroutine SLP simply proceeds from a start pointat block 500 to a block 502 where it calculates the difference betweenDATA,(X+1) and DATA,(X-1) and places the result in the aforementionedregister ACCUM.

As shown in FIG. 17C, subroutine SLP simply proceeds from a start pointat block 500 to a block 502 where it calculates the difference betweenDATA,(X+1) and DATA,(X-1) and places the result in the aforementionedregister ACCUM. The difference thus placed in ACCUM is of courserepresentative of the gradient of the fully smoothed light intensitycurve at pixel X. It should be noted that, although at block 481 (FIG.17B) subroutine SLOPE is analyzing data proceeding from the middle ofFIG. 16B to the left, the difference calculated by subroutine SLP hasthe usual algebraic sign i.e. a positive value in ACCUM following block502 indicates a curve which is increasing from left to right. Followingblock 502, subroutine SLP is exited at block 504 back to subroutineSLOPE.

On leaving block 481 in FIG. 17B, subroutine SLOPE proceeds to block482. The designation "FLG. N=0?" in block 482 means that this blocktests the most significant bit of the 8-bit number placed in ACCUM byblock 502 in FIG. 17C to see if this bit is equal to zero. As previouslyexplained with reference to 463, the 6502 microprocessor used in theAIM-65 computer normally uses the the most significant bit as a signbit. Thus, block 482 is actually testing the sign of the gradientcalculated by subroutine SLP. So long as the video data being processedrelate to the left-hand zone 362 in FIG. 16B, the gradient of the fullysmoothed light intensity curve is always positive and thus operation 482generates a positive result and the program simply loops back from block482 to block 477. However, after repeated passes through block477,478,481 and 482, subroutine SLOPE will reach the transition betweenzone 362 and zone 364, pass through the local intensity minimumassociated with the weld pool edge and enter zone 364, in which thecurve has a negative gradient. Thus, as soon as zone 364 is entered,operation 482 produces a negative result and the program proceeds toblock 484 where M is tested to see if it is equal to zero. Whensubroutine SLOPE first reaches block 484, M will be equal to zero,having previously been set to zero at block 471, and thus block 484 willproduce a positive result and the program will proceed to block 486,where the value of X, which now represents the location of the left-handedge of the weld pool, is written into a hexadecimal register $WDL. Fromblock 486, the program proceeds to block 488, which is identical toblock 484 and thus, when subroutine SLP first reaches block 484 thisblock will produce a positive result, causing the program to proceed toblock 489 where M is incremented to 1. The program then loops back fromblock 489 to block 472.

Subroutine SLOPE now proceeds to find the right-hand edge of the weldpool proceeding to blocks 472-478 in the same manner previouslydescribed, except that subroutine EVALP will now increment X rather thandecrement this counter. Accordingly, on this second pass through blocks472 through 478, subroutine SLOPE will examine the fully smoothed lightintensity data beginning from approximately the center of zone 360 inFIG. 17B and proceeding from left to right in that figure until itreaches the point which the right-hand zone 362 is no longer saturated.Upon reaching 478 for the second time, block 478 will of course producea negative result since M is now equal to 1 and accordingly the programwill proceed from block 478 to block 479, which is identical to block481 and executes subroutine SLP. Since the line intensity data nowrelate to the right-hand zone 362 in FIG. 16B, the slope value generatedby subroutine SLP at block 479 will be negative. Accordingly, block 479is followed by a block 480, which tests the sign of the gradientgenerated by subroutine SLP to see if this gradient is negative. If so,the program simply loops back to block 477 and proceeds to loop throughblocks 477-480 until the boundary between zones 362 and 366 in FIG. 16Bis reached, at which point the gradient becomes positive, block 488produces a negative result, and the program proceeds to block 484. SinceM is now equal to 1, block will produce a negative result and theprogram will proceed, at block 485, to write the value of X, which nowrepresents the location of the right-hand weld pool edge, into aregister $WDR.

From block 485, the program again proceeds to block 488. Since M is nowequal to 1, this block will produce a negative result and the programwill thus proceed to block 490, where M is restored to 0, the differencebetween $WDR and $WDL, which represents the width of the weld pool, iscalculated and placed in a width register $WIDTH, and all positions ofTABLE are filled with zeroes. Next, at block 492, X is set equal to $WDRand then, at block 494, $75 is placed in TABLE,X and X is decremented.The decremented value of X is then tested at block 496 to see if it isequal to $WDL. If not, the program loops back to block 494. It will beapparent to those skilled in the art that the combined effect of blocks490, 492 and 494 and 496 is that the values in TABLE will be 0 forvalues of X less than $WDL and greater than $WDR (i.e. for areas outsidethe weld pool as found by the program) and $75 for all values X from$WDL to $WDR inclusive (corresponding to pixels within the weld pool asfound). Thus, the values in TABLE by the time operation 494 hasdecremented X to be equal to $WDL constitute a square wave which is lowoutside the weld pool, high inside the weld pool and thus has itstransitions at points corresponding to the weld pool edges. At thispoint, block 496 produces a positive result and subroutine SLOPE isexited via block 498.

This completes the sequence of subroutines represented by block 469 inFIG. 17. Accordingly, upon leaving subroutine SLOPE, the computerproceeds to block 650 in FIG. 17 where the tables DATA and TABLE are fedto the two separate traces of the double-trace oscilloscope 72 (FIG. 4).The subroutine used for this purpose is of a type which will be familiarto those skilled in the art and therefore will not be further described.It will be seen from the foregoing description of FIGS. 17A-17H that thedata thus output to the oscilloscope at block 650 represent the fullysmoothed light intensity data placed in table DATA by subroutines SMTHand TRANSF, and the square wave form having its transitions at the weldpool edges, which have been placed in TABLE by subroutine SLOPE.Accordingly, the two traces on the oscilloscope enable the operator tomake a visual check of the correctness of the weld pool edges located bythe software. Following block 650, program PWDTHX proceeds through block652, 654 and 656 as previously described.

FIG. 18 shows the apparatus used to control weld pool width inaccordance with the invention. It will be seen from the description ofFIG. 19 below, that FIG. 18 is in essence a slightly simplified versionof the apparatus shown in FIG. 19; thus a single apparatus can be usedfor both control of the weld pool width and control of the mass andfrequency of the weld pool.

The apparatus shown in FIG. 18 comprises a robot control computer 600which is in two-way communication via lines 90 (also shown in FIG. 4)with the process control computer 80. The robot control computer 600 hasa current command output line which controls the current produced by aconstant current welding supply 602, which supplies current to a weldingassembly comprising an electrode 606 and a workpiece or weldjointpreparation 608. The arc voltage between the electrode and the weldjoint or preparation sensed by means of a pair of arc voltage sensinglines which are connected from the electrode and weld joint preparationrespectively to the robot control computer 600. The robot controlcomputer is also provided with output lines by which it can control themovement of the electrode 606 in at least two dimensions by means of aZ-axis translator and a X-translator 604. Obviously, a Y-axis translatorand appropriate output line from computer 600 can be provided ifdesired. The differential width signals generated at block 658 (FIG. 17)are supplied to the computer 600 (FIG. 18) via the lines 90 and causethe computer 600 to control the current supply 602 so as to adjust theweld pool width towards the desired value.

It will be appreciated that the apparatus and software shown in FIGS.4-18 can, for experimental purposes, be operated on data supplied to thevideo computer interface 100 (FIG. 4) via the line 82 rather than livefrom the video camera 68. Accordingly, the apparatus can be used toreconstruct how the parameters of weld pool width varied during thecourse of a test weld, even when no actual welding operation is takingplace. Obviously, for commercial purposes, it will normally be desiredto use the apparatus during actual welding operation, although theability to make determinations of weld pool width ex post facto may beuseful in certain circumstances for diagnostic or testing purposes.

WELD POOL OSCILLATION METHODS, WELD POOL MASS CONTROL METHOD AND WELDPOOL MASS/FREQUENCY MEASURING APPARATUS

The weld pool oscillation methods and the weld pool mass control methodof the invention all depend upon the fact that, like any mass of liquid,a weld pool has a natural frequency of oscillation which is related tothe mass and density of the pool. By the techniques of the instantmethod, the natural frequency of oscillation of the weld pool may bemeasured, thereby producing a measurement of the mass of the pool.Repeated measurements of the natural frequency at spaced intervalspermit changes in the frequency, and thus in the mass of the weld poolto be detected, and thus permit control of the mass of the weld pool.Furthermore, it will be apparent to those skilled in the art that,because weld pools tend to maintain a substantially constant geometry,the mass of the weld pool will be a function of the width of the weldpool and the depth thereof, this depth being equal to the weldpenetration. Accordingly, measurements of both weld pool mass and widthby the techniques of this invention permit calculation of weld pooldepth and weld penetration, and thus allow for the control of weldpenetration.

More specifically, it has been discovered that the welding arc itselfexerts a downward force on the weld pool, thereby causing a depressionof the upper surface of the weld pool. The downward force of the arc,and thus the amount of depression of the weld pool, has been found to bedependent upon the welding current. Accordingly, if the welding currentis pulsed (i.e. the value of the current changed substantially for arelatively brief period) or if the arc is abruptly removed from the weldpool, the resultant change in downward force acting on the weld poolcauses the weld pool to oscillate at its natural frequency. Thisoscillation of the weld pool will continue even after the originalwelding conditions are restored, that is to say after the pulse in theweld current is finished or after the arc is restored to the pool, thuspermitting the natural frequency of oscillation to be measured after thetransient phenomena which induced the oscillation have terminated, andallowing the mass of the weld pool to be measured in the absence of thetransient disturbance and the mass of the weld pool under thesteady-state welding conditions determined.

FIGS. 19-34 of the accompanying drawings show the presently preferredweld pool mass/frequency measuring apparatus of the invention used tocarry out the measurements already described, including the necessarysoftware. It should be noted that the apparatus and software shown inFIGS. 19-34 is only desiged to measure the frequency of oscillation of aweld pool. However, the apparatus and software shown in FIGS. 19-34 areso arranged that a single set of welding apparatus may incorporate boththe frequency-measuring apparatus shown in FIGS. 19-34 and the weld poolwidth measuring apparatus previously described, thereby permittingsimultaneous measurement of weld pool width and oscillation frequency,as required for controlling weld pool depth and hence weldingpenetration. In practice, it may often not be necessary tosimultaneously measure weld pool oscillation frequency and width, sinceit has been found empirically that a relationship exists betweenfrequency, weld pool width and depth and arc length as follows:

    F=19.14, W.sup.0.033 D.sup.-0.77 H.sup.- 0.35,

where:

F is the oscillation frequency in Hertz;

W is the weld pool width in inches;

D is the weld pool depth (weld penetration in inches);

H is the arc length in inches.

Accordingly, if oscillation frequency and arc length are held constant,control of weld pool depth and weld pool penetration can be achievedwithout direct measurement of weld pool width.

Obviously, if accurate measurements of weld pool oscillation frequencyare to be achieved, all external driving forces which might affect theoscillation of the weld pool must be reduced to a minimum. One likelysource of significant external driving forces which would interfere withmeasurement of weld pool frequency is variations in the power supply tothe welding apparatus. Accordingly, the apparatus shown in FIGS. 19-25makes use of a linear power supply in order to eliminate cyclicaberrations normally present in full-wave or half-wave recitifiedwelding power supplies. Also, this apparatus includes various specialsmoothing circuits to smooth the power supply so that the onlymeasurable oscillations in the weld pool occur at the natural frequencyof the pool. In addition, the apparatus includes special circuitry toeffect pulsing of the welding current, since this has been found to bethe most convenient technique for inducing oscillation of the weld pool.

As shown in FIG. 19, the preferred weld pool mass/frequency measuringapparatus of the invention comprises a constant voltage power supply(transformer/rectifier) 700, which is of a commercially-availablethree-phase type, and a constant current power supply(transformer/rectifier) 698, which is also of a commercially-availablethree-phase type, the two power supplies being connected in parallel.The two power supplies are used because the instant weld pooloscillation methods require controlled variation in the welding current,and such variation is effected by regulation of the constant voltagepower supply as described below. However, it is difficult to procureconstant voltage power supplies with sufficient capacity to effectcommercial-sized welds. Accordingly, the constant current and constantvoltage power supplies are used in parallel, the constant current powersupply supplying the bulk of the welding current while the constantvoltage power supply effects the necessary variation in the weldingcurrent. To ensure that no reverse flow of current can occur through aregulator model 702 (described below) because of the interconnection ofthe two power supplies, a diode 699 is connected between the negativeterminal of the constant current power supply 698 and the end of theregulator module 702 remote from the negative terminal of the constantvoltage power supply 700. The positive terminals of the power supplies698 and 700 are connected via an in-line shunt 706, which permitsmeasurement of actual welding current, to a "weld joint preparation"707. (As explained below, for experimental purposes a bead-on-platewelding operation, which does not actually join two pieces of metaltogether, was performed, and thus integer 707 comprised only a singlemetal plate. Under commercial conditions, the weld joint preparation 707would of course comprise the two metal portions to be welded together.)The line joining the shunt 706 to the weld joint preparation 707 isconnected to a true earth ground 709. The negative terminal of the powersupply 700 is connected via a regulator module 702 and a supply line 703to a welding electrode 708, which is the non-consumable tungstenelectrode normally used in a gas tungsten arc welding apparatus. Theelectrode 708 is also connected directly to the negative terminal of thepower supply 698. The electrode 708 is movable vertically relative tothe weld joint preparation 707 by a Z-axis positioner 712 and parallelto the horizontal upper surface of the weld joint preparation 707 bymeans of a Y-axis positioner 717. Both positioners 712 and 717 arescrew-type positioners including stepper motors which rotate onerevolution for each cycle of a phased square wave train input, thenecessary square wave inputs being provided by a Z-axis translator 716and a Y-axis translator 714 respectively. Both the translators 714 and716 are of the commercially-available Summit 8083 type. The regulatormodule 702 is controlled by a control module 704 via a control line704A. The control module 704 is connected to the shunt 706 by a pair oflines 705A and 705B, which provide the control module 704 with thepotentials at either end of the shunt 706; there exists between the line705A and 705B a voltage which is proportional to the actual weldingcurrent passing through the shunt 706. The control module 704 is alsoconnected by a line 705C to the line joining the shunt 706 to thepositive terminals of the power supplies. This line 705 furnishes aground for the control module 704. The control module also receivessignals on a pair of lines 701A and 701B from an analog output isolationunit 724, and transmits ±15 V and ground to the unit 704 via amulti-line connector 701C. The analog output isolation unit 724 formspart of an interface assembly which also includes a digital/analogconverter 722, an analog/digital converter 726, an analog inputisolation unit 728 and a parallel input/output unit 730. As indicated inFIG. 9, the analog output isolation unit 724 receives signals from thedigital/analog converter 722, and the analog/digital converter 726receives signals from the analog input isolation unit 728. The interfaceassembly is itself connected via a two-way bus 729 to a process controlcomputer 734. The computer 734 is a Rockwell AIM-65 digital computer,which is identical to the computer 80 described above with reference toFIGS. 4 and 5. The analog input isolation unit 728 is also connected tothe welding electrode 708 via a line 731A and to the weld jointpreparation 707 via a line 731B; thus, the analog input isolation unitreceives signals on line 731A and 731B indicative of the actual voltageexisting between the welding electrode and the weld joint preparation.The parallel/input output unit 730 is connected via a two-way bus 727 toa parallel input/output isolation unit 718. This unit 718 suppliesZ-axis step and Z-axis direction signals to Z-axis translator 716 vialines 719A and 719B respectively. Similarly, the unit 718 suppliesY-axis step and Y-axis direction signals to the Y-axis translator 714via lines 721A and 721B respectively. Finally, as indicated in the lowerleft-hand portion of FIG. 19, the unit 718 is in two-way communicationwith a pendant, by means of which an operator can control an operationof the welding apparatus and sends output signals to a translator powerunit. If desired, the unit 718 may optionally be arranged to control thewater and gas solenoids and the power supply contactor of the apparatus,as indicated within the broken boundary in FIG. 19. However, in practiceit has been found that these solenoids and contactor can be controlledby the operator himself without inconvenience, and thus the optionalconnections to unit 718 shown in FIG. 19 have not been included in thepresent form of the apparatus.

Parts of the apparatus shown in FIG. 19, and especially the controlassembly comprising unit 722, 724, 726, 728 and 730, together with theunit 718, are shown in more detail in FIG. 20, in which 718C and 718Drepresent sub-units of the unit 718 and 730A and 730B subunits of theunit 730, shown in FIG. 19. As shown in FIG. 20, the Rockwell AIM-65computer 734 receives a tape input program; this program is fed to theJ1 connector of the computer on pins L and M, with a ground line beingprovided to pin 1 of the same connector. The computer 734 communicatesvia a ribbon connector 735 with a buffer 738, which is in turn connectedto the aforementioned bus 729, which has the form of the second ribbonconnector. The buffer 738 and the two associated ribbon connectors 739and 735 comprise a standard, commercially-available Rockwell RM65-7104double-ribbon buffer system. The ribbon connector 735 is connected tothe J3 connector on the expansion bus of the Rockwell AIM-65 computer734.

The ribbon connector or bus 729 is connected to a card cage 736, whichis a standard, commercially-available Rockwell RM65-70116 card cage.Further details of the RM65-7104 double-ribbon buffer system and theRM65-7016 card cage may be obtained from the manufacturer's literature.The card cage 736 not only serves to provide communication between thecomputer and the various parts of the control assembly and the unit 718,but also physically holds the remaining pats of the control assembly andunit 718, the various circuits on these unit being mounted on cardswhich are inserted into the card cage 736 in a manner which will befamiliar to those skilled in the art. The units actually mounted withinthe card cage 736 are enclosed within the broken boundary in FIG. 20.

As shown in FIG. 20, the computer 734 communicates via the buffer 738and the card cage 736 with the digital/analog converter 722 of thecontrol assembly, this digital/analog converter 722 comprising astandard, commercially-available Gordos Model DA-410 circuit board,which is mounted on slot number 3 of the card cage 736. Connector c ofconverter 722 is connected to connector a of analog output isolationunit 724, which is mounted in slot number 1 of the card cage 736. Aspreviously described, unit 724 is connected, via its connector b andlines 701A, 701B and 710C with control module 704. The output fromconnector b of unit 724 on lines 701A and 710B can also be fed to anoscilloscope (not shown) to be described below. The isolation unit 724is necessary to provide signal isolation from the high power weldingcircuits themselves.

The computer 734 also communicates via buffer 738 and card cage 736 withthe analog/digital converter 726, which is a standard,commercially-available Gordos Model AD-10 circuit board mounted in slotnumber 10 of card cage 726. Connector g of converter 726 receivessignals from connector j of the analog input isolation unit 728, whichis mounted in slot number 12 of the card cage 736. The outputs fromconnector j of unit 728 can also be supplied to the same oscilloscope asthe signals from connector b of unit 724 as an indicator of the arcvoltage. As described above with reference to FIG. 19, the unit 728receives signals on lines 731A and 731B representative of the weldingarc voltage and welding arc current, these inputs being received atconnector h of unit 728. The analog/digital converter 726 has thecapability for 16 single-ended or 8 double-ended input channels with a0-10 V input signal range providing a resolution of 10 mV.

Also as shown in FIG. 20, the computer 734 communicates via buffer 738,card cage 736 and the bus 727 with two input/output units 730A and 730B,which form part of unit 730 shown in FIG. 19. The input/output units730A and 730B are mounted in slots numbers 5 and 16 respectively of cage736. Unit 730A is a standard, commercially-available Gordos GBPI/Ocircuit card, while unit 730B is a Rockwell RM65-5222 circuit board.Connector d of unit 730A communicates with connector q of an Isolation Aunit 718C, which also forms part of the unit 718 shown in FIG. 19. Unit718C is a standard, commercially-available Gordos Model PB-16 circuitboard which is mounted on the right inside surface (in front view) ofthe card cage 736. Connector r of unit 718C handles communications withthe pendant and also handles the outputs on lines 721A and 721B to thetranslator 714 which feeds its output to stepper motor number 1, themotor of y-axis positioner 717. Similarly, connectors k, n, m, and p ofinput/output unit 718B are connected to connector s of an isolation unitB, 718D, the second major portion of the unit 718 shown in FIG. 19. Unit718D is a second standard, commercially-available Gordos Model PB-16circuitboard, which is mounted on the opposite surface of the card cage736 from the unit 718C i.e. unit 718D is mounted on the left insidesurface of the card cage as seen from the front thereof. Connector t ofunit 718D is connected via lines 719A and 719B to the translator 716, asalready described, and the output from translator 716 is fed to steppermotor number 2, the motor of z-axis positioner 712. Unit 718D alsocommunicates with the translator 714. (The connections among theisolation units 718C and 718D, the translators 714 and 716 and thestepper motors are simplified in FIGS. 19 and 20 for purposes ofillustration. In fact, each translator receives power, direction, clockand common connections from the associated isolation unit and isconnected to its associated stepper motor via a six-line connector. Asexplained in more detail below, isolation unit 718D only supplies thepower connection to the Y-axis translator 714, the other threeconnections to translator 714 being handled by isolation unit 718C.)

FIG. 21 shows in more detail the components shown in the lower righthand corner of FIG. 19. The constant voltage power supply 700 is aconstant voltage, 3-phase power supply of the full-wave rectified type,being a National Cylinder Gas Companying Model DRCV-5 with a capacity of35 volts, 500 amps. As previously mentioned, the negative terminal ofthe power supply 700 is connected to the regulator module 702. Thismodule 702 comprises 32 resistor-transitor combinations, only one ofwhich is shown in FIG. 21 for the sake of simplicity. Theseresistor-transistor combinations will be described in more detail belowwith reference to FIG. 23; for present purposes it is sufficient to notethat each combination comprises a low value resistor R29 connectedbetween the negative terminal of the power supply 700 and the emitter ofa power transistor 748, which is a standard, commercially-availableMotorola 2N6284 power transistor. The collector of each power transistor748 is connected via the line 703 to the welding electrode 708 asalready described, while the base of each transistor 748 is connectedvia a resistor R30 and the line 704A to the control module 704.

As explained above with reference to FIG. 19, the line 705B from thecontrol module to the line joining the positive terminal of the powersupply 700 to the shunt 706 provides a system ground. The lines 705A and705B from the control module 704 are connected to opposed ends of theshunt 706 so that, as already mentioned, a potential difference existsbetween the line 705A and 705B proportional to the welding current whichflows through the shunt 706. Also as already mentioned, the end of theshunt 706 remote from the power supply is connected to the weld jointpreparation 707 and to the true earth ground 709. The control module 704also receives, on lines 701A and 701B, an analog "set point signal",which is ultimately derived from a digital signal originating in thecomputer 734 and represents the desired welding current, and the controlmodule supplies power to the digital/analog converter unit 724 (FIGS. 19and 20) via the multi-line connector 701C.

Further details of the circuitry of the regulator module 702 are shownin FIG. 23. The 32 power transistors 748, together with theiraccompanying resistors R29, are arranged in four banks each containingeight transistors. Each of the four banks of transistors is mounted in afan-cooled heat sink module as shown in FIG. 23. As shown in thatfigure, the supply line from the negative terminal of the power supply700 is connected to one terminal of each of eight resistors R29A-Harranged in parallel. These low value resistors R29, which areconveniently given the value of 1 ohm, are provided to limit the maximumcurrent which will pass through any one of the transistors 748. Althoughin theory the transistors 748 each receive identical base voltages andhave identical gain characteristics, in practice not all the transistorswill have exactly identical gains, so that a larger share of the weldingcurrent will be carried by those transistors having a high gain. Toreduce the possibility of damage to transistors having high gain, theresistors R29 are inserted, thereby limiting the current carried by thehigh-gain transistors to an acceptable level. The terminal of each ofthe resistors R29A-R29H remote from the power supply 700 is connected tothe emitter of its associated transistor 749A-749H, the base of eachtransistor being connected via a high resistor R30A-R30H to the line704A as already described. The collector of each of the transistors748A-748H is connected to the line 703. A fan 749, having normal 120 VACpower connections, is provided to cool the transistors 748 and theirassociated resistors R29.

FIG. 22 shows the power supply circuitry comprising the control module704 shown in FIGS. 19, 20 and 21. In view of the relative complexity ofthis circuitry and the number of variable parameters involved, it isbelieved that the details of this circuitry will be more readilyappreciated if consideration is first given to the type of output whichit is designed to produce. This output is illustrated in the upper halfof FIG. 26, which is a graph of arc current against time. It will beseen that the arc current desired comprises a steady base current levelon which are superimposed regularly-spaced square pulses. The parameterswhich defined this type of current pattern are the base current level,the pulse current level, i.e. the current level during these squarepulses, the pulse duration and the pulse frequency (which mayalternatively be specified as the delay between successive pulses). Thecircuitry shown in FIG. 22 is designed so that each of these pulses canbe adjusted individually. The circuitry shown in FIG. 22 makes extensiveuse of multi-pin connectors, the pins of which are designated by anomenclature TSX-Y, in which X represents the number of the connectorand Y the number of the pin.

The lower part of FIG. 22 shows the power supply circuitry used in thecontrol module. Power is supplied to a Polytron Devices Model P33±-15 Vpower supply 741 from a conventional single-phase mains 120 VAC supply.In order to limit undesirable effects due to voltage transients in themains supply, the mains supply leads are bridged by a pair ofbreakthrough diodes D4 and D5 which have their cathodes connectedtogether and their anodes connected to the opposed mains supply lines.Diodes D4 and D5 limit the maximum voltage across the power supplyinputs to approximately 130 V. The mains supply lines are also bridgedby a smoothing capacitor C21.

The power supply 741 produces the conventional +15 V, -15 V and groundoutputs. For smoothing purposes, the +15 V and ground supply lines arebridged by capacitors C22, C23 and C24 connected in parallel, thesethree transistors totaling 0.45 microfarad. Similarly, the -15 V andground lines are bridged by capacitors C25 and C26, these two capacitorsbeing connected in parallel and totaling 0.35 microfarad. The groundoutput of power supply of 741 is fed to connectors TS2-2 and TS2-5. The+15 V output of power supply 741 is fed to connector TS2-1 and is alsofed via a potentiometer P1 (used as a variable resistor) to connectorTS2-4. The -15 V output from power supply 714 is fed to connector TS2-3.

The circuitry in the upper part of FIG. 22 will now be described. Line701A, which carries a signal originally generated by the computer 734and converted to analog form by the converter 722 (FIG. 20), this signalrepresenting the desired base current set by the operator by means ofsoftware described below, is connected to one fixed terminal of apotentiometer P7, the other fixed terminal of which is grounded.Potentiometer P7 serves to allow adjustment of the base current setting.The moveable terminal of potentiometer P7 is connected via a resistorR40 to pin 6 (the negative input) of an amplifier 750, which is of theLM324J type manufactured by National Semiconductor. Similarly, line701B, which carries a signal originally generated bythe computer 734 andconverted to an analog form by the converter 722 (FIG. 20), this signalrepresenting the desired pulse current set by the operator by means ofthe software described below, is connected to one fixed terminal of apotentiometer P9, the other fixed terminal of which is grounded.Potentiometer P9 serves to allow adjustment of the pulse currentsetting. The moveable terminal of potentiometer P9 is connected via aresistor R41 to pin 6 of amplifier 750. Pin 5, the positive input ofamplifier 750 is grounded via a resistor R42. The output from pin 7 ofamplifier 750 is fed to one fixed terminal of a potentiometer P10, theother fixed terminal of which is grounded. The moveable terminal ofpotentiometer P10 is connected via a resistor R43 to pin 6 of amplifier750. As will be apparent to those skilled in the art from the foregoingdescription of FIG. 26, the computer provides the base current signalcontinuously to potentiometer P7 while welding is being performed, butonly supplies the pulse current signal during the interval when thecurrent pulses are present.

Pin 7 of amplifier 750 is connected via a resistor R44 to pin 9 of anamplifier 744, which is again of the LM324J type. Two other circuitsalso supply inputs to pin 9 of amplifier 744. In the first of thesecircuits, connector TS1-6 is connected to ground via resistors R45 andR46 connected in series. The mid-point of the bridge formed by resistorR45 and R46 is connected to one side of a potentiometer P11 which isused as a variable resistor. The same terminal of P11 is connected via acapacitor C28 to terminal TS1-10, and is also grounded. The terminal ofpotentiometer P11 remote from terminal D is connected via resistor R47to pin 9 of amplifier 744. Terminals TS1-6 and TS1-10 are spare inputterminals provided to allow testing of the control module circuitrywithout inputs from the computer.

The last input to pin 9 of amplifier 744 is provided by an amplifier742, which is again of the LM324J type. Pins 2 and 3 of amplifier 742are connected via resistors R50 and R48 respectively to the lines 705Aand 705B from the shunt 706. Thus the normal input to amplifier 742 is asignal representing the actual welding current. To limit the possibleinputs to amplifier 742, the fixed terminals of a potentiometer P13 areconnected to the ±15 V supply lines and the movable terminal of P13 isconnected via a resistor R51 to pin 2 of amplifier 742. In addition, pin3 of amplifier 742 is connected via a resistor R49 to one side of apotentiometer P12 used as a variable resistor, the opposite side of P12being grounded.

Amplifier 742 receives the conventional power connections, +15 V at pin4 and -15 V at pin 11 and its output from pin 1 is fed back to its pin 2via a resistor 52. The output from pin 1 of amplifier 742 is also fedvia resistor R53 to pin 9 of amplifier 744.

Pin 10 (the positive input) of amplifier 744 is grounded via a resistorR54. The output from pin 8 of amplifier 744 is fed back to pin 9 thereofvia a resistor R55. The output from pin 8 of amplifier 744 is alsoconnected to one fixed terminal of a potentiometer 314, the other fixedterminal of P14 being grounded. The movable terminal of P14 is connectedvia a resistor R56 to pin 13 (the negative input) of an amplifier 746,which is again of the LM324J type. Pin 12 of amplifier 746 is groundedvia a resistor R37. The output from pin 14 of amplifier 746 is fed viaresistors R56 and R39 connected in series to the base of a transistor755, of the commercially-available 2N6126 type. The emitter oftransistor 755 is connected to ground via a resistor R35. The collectorof transistor 755 is connected to each of the 48 base resistors R30present in the regulator.

The feedback arrangement of amplifier 746 is somewhat complicated, threeseparate parallel connections being made from between resistors R57 andR39 to pin 13 of amplifier 746. The first of these three parallelconnections includes a breakthrough diode 745 of thecommercially-available IN4741 type, rated at 11 V, 500 mW. The secondparallel connection comprises a capacitor C29. The third parallelconnection includes a capacitor C30, a fixed resistor R58 and apotentiometer P15 (used as a variable resistor) all connected in series.

FIG. 24 shows the circuitry of the analog input isolation unit 728 shownin FIGS. 19 and 20. As previously mentioned, this circuitry is insertedin slot number 12 of the card cage 736 (FIG. 20), receives its inputsvia connector h and transmits it outputs on connector j to connector gof the analog/digital converter 726.

As shown in FIG. 24, the analog input isolation unit 728 comprises twoseparate circuits, namely a voltage isolation (DC coupled) circuit shownin the upper part of FIG. 24 and an arc voltage AC coupler circuit shownin the lower part of FIG. 24.

The card cage 736 (FIG. 20) is provided on its rear panel with fiveseparate 2×10-pin connectors which are used to make the externalconnections to the control assembly. In a manner similar to that usedfor the multi-pin connectors on the control module 704 described above,hereinafter "PBX-Y" designates pin Y of connector X on the rear panel ofthe card cage. Where necessary, the left- and right-hand pins of eachpair will be identified by suffices L and R respectively. Those skilledin the art will be aware that in such connectors the pins in each pairare bridged to effect the electrical connections. Each of the cardsinserted in the card cage 736 also has its own multi-pin connectorswhich will be described individually with reference to the variouscards, but it should be noted that a similar nomenclature will be usedfor these connectors; for example j-12 denotes connector j, pin 12. Thevarious power supplies required by the circuits in the control assemblyare provided either by the computer 734 or, in the case of the outputside of the unit 724 via the multi-line connector 701C. The power supplycircuits will not be described in detail, since it is believed thatappropriate stabilized power supply circuits will readily be apparent tothose skilled in the art. The +15 V supply from connector 701C isreceived at connector TB1-8, the ground supply at TB1-9 and the -15 Vsupply at connector TB1-10.

The analog input isolation unit 728 is provided with a 7-pin in-lineconnector designated h and a 50-pin 2×25 line connector designated j.Connector h-1 receives +12 V from a stabilized power supply (not shown),connector h-2 receives the common or ground line from the same supplyand connector h-3 receives the -12 V line from the same supply.Connector j-2 receives +15 V from connector TB1-8, connector j-4receives -15 V from connector TB1-10 and connector j-6 is connected tothe ground connector, TB1-9. The other connections to connectors h and jare described individually below.

The "positive" arc voltage, hereinafter designated +VARC, received fromthe weld joint preparation 707 (FIG. 19) via line 731B is fed toconnector TB3-1, and thence to connector h-4 on the analog inputisolation unit 728. As shown in the upper part of FIG. 24, thisconnector h-4 is connected to pin 5 of an amplifier 760, which is astandard Model AD289J amplifier manufactured by Analog Devices, Inc. Thenegative arc voltage, taken from welding electrode 708 (FIG. 19) vialine 731A is fed to connector TB3-2, and thence to connector h-5 which,as shown in the upper part of FIG. 24, is connected via a resistor R59to pin 1 of amplifier 760. Pins 1 and 5 of amplifier 760 are bridged bya potentiometer P16 used as a variable resistor.

Amplifier 760 receives the conventional power connections, +12 V at pin6 and ground at pin 7. The positive output from pin 10 of amplifier 760is fed via a resistor R60 to connector j-12. This output placed onconnector j-12 is channel 0 of the input to the analog/digital converter726 (FIG. 19); as indicated in FIG. 24, this connector j-12 is connectedto connector g-39 of converter 726. Pin 9, the negative output, ofamplifier 760 is grounded via an RC circuit comprising a resistor R61and a capacitor C31 connected in parallel. Pin 9 of amplifier 760 isalso connected to the moveable terminal of a potentiometer P17, thefixed terminals of which are connected via resistors R62 and R63 to the+12 V and -12 V supplies respectively. The grounded terminals of R61 andC31 are connected to connector j-28, which provides channel 8 of theinput to the analog digital converter 726 (FIG. 19). As shown in FIG.24, connector j-28 is connected to connector g-23 on the converter 726,and the connectors j-12 and j-28 are bridged by a capacitor C32.

As shown in the lower part of FIG. 24, the +VARC signal from connectorh-4 is fed to pin 1 of an amplifier 726, which is a second AD289Jamplifier identical to amplifier 760 previously mentioned. The -VARCsignal from connector h-5 is fed to one plate of a capacitor C33; theopposed plate of C33 is connected to connector h-4 via a resistor R64and is also connected to one terminal of a single-pole, single-throwswitch S50. The opposite terminal of S50 is connected to pin 5 ofamplifier 762. This pin 5 is also connected to one terminal of a secondsingle-pole, single-throw switch S51. The opposed terminal of S51 isconnected to connector h-4 and is also connected via a resistor R65, apotentiometer P18 (used as a variable resistance) and a resistor R66 topin 4 of amplifier 762. The terminal of R65 remote from S51 is connectedvia a resistor R67 to the moveable terminal of a potentiometer P19, thefixed terminals of which are connected to pins 2 and 3 of amplifier 762.

When the welding apparatus is in use, S50 is closed and S51 is open, asshown in FIG. 24. However, when it is desired to set or change theoffset adjustment on the converter 726, S50 is opened and S51 is closed.

Amplifier 762 receives the conventional power connections, +12 V at pin6 and ground at pin 7. The output from pin 10 of amplifier 762 is fedvia a resistor R68 to connector j-14. This output through connector j-14is channel 1 of the input to the analog/digital converter 726 (FIG. 20)and, as shown in FIG. 24, connector j-14 is connected to connector g-37on the converter 726. Pin 9, the negative output, of amplifier 762 isgrounded and is also connected to connector j-30, which supplies channel9 of the input to the analog/digital converter 726. As shown in FIG. 24,this connector j-30 is connected to connector g-21 on the converter 726.Connector j-14 and j-13 are bridged by smoothing capacitor 34.

The voltage isolation circuit shown in the upper half of FIG. 24 is usedwith the potentiometer p17 set so that the output (the potentialdifference between connectors j-112 and j-28) is approximately 1/3 ofthe arc voltage; this multiplexer is chosen to fit the range of theGordos AD-10 convertor. Capacitor C32 and resistor R32 effect low passfiltering, and we preferably arranged to remove components above about800 Hz. In the AC coupled circuit shown in the lower half of FIG. 24capacitor C33 and resistor R64 effect high pass filtering, removingcomponents below about 5 Hz., while capacitor C34 and resistor R68effect low pass filtering, removing components above about 600 Hz.

FIGS. 25A and 25B show the circuitry of the analog isolation unit 724shown in FIGS. 19 and 20. This circuitry comprises a base currentcommand isolation circuit shown in FIG. 25A, and a pulse current commandisolation circuit shown in FIG. 25B. The circuit shown in FIG. 25A setsthe base current to be maintained during the welding process, while thecircuit shown in FIG. 25B sets the level of the current to be maintainedduring the pulses. This circuitry serves to protect the digital/analogconverter 722 from the high voltage and current transients which mayoccur at the welding electrode 708.

The circuit board carrying the circuits shown in FIG. 25 is providedwith a 7-pin connector a and an 8-pin connector b. Connector b-1receives the +15 V supply from connector TB1-8, connector b-2 receivesthe ground supply from connector TB1-9 and connector b-3 receives the-15 V supply from connector TB1-10. The remaining connections toconnector a and b are described individually below.

As shown in FIG. 25A, connectors a-1 and a-2 receive the positive andnegative outputs respectively from channel 0 of the digital/analogconverter 722 (FIGS. 19 and 20). The potential difference between thesepositive and negative outputs is an analog signal, generated by thedigital/analog converter 722 under directions from the computer 734,which represents the base current which the computer has set under thecontrol of an operator. The positive input from connector a-1 is fed topin 5 of an amplifier 764, which is a Model AD290 amplifier manufacturedby Analog Devices, Inc. The negative input from connector a-2 is fed topins 1 and 6 of amplifier 764. Amplifier 764 receives the conventionalpower connections, +15 V at pin 7 and ground at pin 8. The positiveoutput from pin 12 of amplifier 764 is fed via a resistor R69 toconnector b-4 which is connected via connector TB1-6 to line 701A. Pin11, the negative output, of amplifier 764 is grounded via an RC circuitcomprising a resistor R70 and a capacitor C35 connected in parallel, andis also connected to the moveable terminal of potentiometer P19, thefixed terminals of which are connected via resistors R71 and R72 to the+15 V and -15 V supply lines respectively. Connector b-4 is alsoconnected to ground via an RC circuit comprising a resistor R73 and acapacitor C36 connected in parallel.

The circuit shown in FIG. 25B is identical to that shown in FIG. 25A,except that it receives the positive and negative inputs from channel 1of the digital/analog converter 722 via connectors a-3 and a-4respectively. An amplifier 766, which is a Model AD290 amplifieridentical to the amplifier 764 previously described, receives thepositive input at pin 5, the negative input at pins 1 and 6 and theconventional power connections, +15 V at pin 7 and ground at pin 8. Theoutput from pin 12 of amplifier 766 is taken via a resistor R74 to aconnector b-5 and thence via connector TB1-7 to line 701B. The remainingcomponents of the circuit shown in FIG. 25B, namely resistors R75, R76,R77 and R78, the capacitor C37 and potentiometer P20 are connected in amanner identical to the resistors R70, R71, R72 and R73, the capacitorsC35 and the potentiometer P20 in FIG. 25A; note, however, that there isno equivalent of C36 in FIG. 25B.

Hardware features not shown in the accompanying drawings are as follows.The operator pendant connected to isolation unit A, 718C in FIG. 20 is a4×4 keyboard of a type which will be familiar to those skilled in theart having four drive lines hereinafter referred to as lines 4-7) andfour sensing lines (hereinafter referred to as lines 0-3). Each of theoperator-buttons provided enables a connection to be made between one ofthe drive lines and one of the sensing lines, thereby enabling thependant to be scanned for one input at a time. The buttons provided, andthe lines interconnected are as follows:

    ______________________________________                                        Pushbutton   Lines Interconnected                                             ______________________________________                                        Direction    4-0                                                              X jog        4-1                                                              Y jog        4-2                                                              Z jog        4-3                                                              Weld start   5-3                                                              Weld stop    6-3                                                              ______________________________________                                    

At present, of course, since no X-translator is provided on theapparatus the X jog button is not useable; however, this button isprovided for future expansion. The direction "button" has the form of atoggle switch which will remain in either of its positions when set bythe operator. The remaining operator buttons are push-button switcheswhich are biased open but can be held closed by the operator.

As previously mentioned, communications between the computer 734 and thependant are made via the input/output unit 730A and the isolation A unit718C in FIG. 20. More specifically, pendant lines 0-7 are connected tolines 0-7 of Port A of unit 730A. Communication between port A of unit718C and the pendant is established via the 32-line connector r on unit718C and connector TB5, the exact connections being as follows:

    ______________________________________                                        Port A,  Connector r, Connector TB5,                                                                            Pendant                                     Line No. Line No.     Pin No.     Line No.                                    ______________________________________                                        0        1            4           0                                           1        3            3           1                                           2        5            2           2                                           3        7            1           3                                           4        10           8           4                                           5        12           7           5                                           6        14           6           6                                           7        16           5           7                                           ______________________________________                                    

Port A of unit 730A is addressed by the computer 734 by the hexadecimaladdress 9C01.

Lines 2, 4, 6 and 8 of connector r are grounded, while lines 9, 11, 13and 15 receive +5 V from a stabilized power supply. Lines 17-26 ofconnector r are not used.

Port B of unit 730A (addressed by the computer address 9C00), lines 0-5are not used. Line 6 of this port carries a Y-axis translator clocksignal, which is passed via connectors r-29 and r-31 and connector TB4-7to pin 1 of the Y-axis translator 714. Line 7 of the same port B carriesa Y-axis translator direction signal which is passed via connectors r-27and TB4-10 to pin 2 of the Y-axis translator 714. Lines 28, 30 and 32 ofconnector r receive the common return from the Y-axis translator viaconnector TB4-5.

Port 1B of unit 730B (addressed by the computer as 9D00), lines 0, 1 and6 are not used. Line 2 of the same port carries a Z-axis translatorpower signal, which is fed via connectors t-6 and TB2-10 to fuse 3 ofthe Z-axis translator 716. Line 3 of port 1B carries a Y-axis translatorpower signal which is fed via connector t-8 and TB4-10 to fuse 1 on theY-axis translator 714. Line 4 of port 1B carries a X-translator powersignal which is fed via connectors t-10 and TB3-10; however, since noX-axis translator is provided, the latter connector is not actuallyconnected, this feature being provided for later development of theapparatus. Similarly, port 1B line 5 carries a X-axis translatordirection signal which is taken to connector t-12 but not used. Line 7of port 1B carries a X-axis translator clock signal which is taken toconnectors t-16 and TB3-7L but not used.

Port 2B (addressed as 9D10) of unit 730B lines 0-4 and 6 are not used.Line 5 of port 2B carries a Z-axis translator direction signal, which isfed via connector t-28, which is fed via connector TB2⁻¹⁰ to pin 2 ofthe Z-axis translator 716. Line 7 of port 2B carries a Z-axis translatorclock signal, which is fed via connectors t-32 and TB2-7 to pin 1 of theZ-axis translator 716.

The remaining connections to connector t are as follows. Lines 5, 7 and9 of connector t are connected to the live side of a 115 VAC powersupply. Lines 11 and 15 are designed to receive the common return fromthe (presently non-existant) X-translator and are connected to connectorTB3-5. Lines 27 and 31 of connector t receive the common return from pin5 of the Z-axis translator 716 via connector TB2-5.

In unit 718C, modules 0-3 and 14 are standard D.C. input modules, whilemodules 4-7, 13 and 15 are D.C. output modules. Modules 8-12 are empty.In unit 718D, modules 0, 1, 6, 8, 9, 10, 11, 12 and 14 are not used.Modules 2-5 are standard AC output modules and modules 7, 13 and 15 arestandard DC output modules.

Connections via the TB connectors not previously discussed are asfollows. In connector TB1, pins 1-5 are not used. Connector TB2, lines1-3 are not used, while line 4 is grounded. Line 5 left and right servesto convey the common return from the Z-axis translator 716 to connectort-15. As already mentioned, lines 6-10 carry the signals from the Z-axistranslator to the stepper motor.

The connector TB3, line 3 is grounded, while line 4 is a shield line.Line 5 provides the common return from the X-translator, when used, toconnector t-7. Lines 6-10, which are intended to be connected to aX-axis translator are not used.

In connector TB4, lines 1 and 2 are not used. Line 3 serves as a shieldline while line 4 is the ground line. Line 5 serves to convey the commonreturn from the Y-axis translator 714 to connector r-13. As alreadymentioned, lines 6-10 carry the various signals to the Y-axis steppermotor from the Y-axis translator 714.

In connector TB5, lines 1-8 are used, as already described, to establishconnections between the connector r and the pendant lines. Line 9connects the pendant ground to the other ground lines, and line 10 isnot used.

The analog/digital converter 725 is addressed by the computer 732 asaddress 9E0X (when X is any hexadecimal digit). The two channels of thisconverter have already been described above. The digital/analogconverter 722 is addressed by the computer by addresses 9F0X. Inaddition to the channel 0 and 1 already discussed, this converterprovides on channel 2 a DC sample data output and on channel 3 a DC pooloscillation output.

As previously mentioned, the upper part of FIG. 26 shows the form of arccurrent used in the instant weld pool oscillation methods, this arccurrent comprising a steady base current on which are superimposedsquare-wave pulses of a pre-determined duration and frequency. The lowerpart of FIG. 26 shows the corresponding arc voltage/time graph, the twoparts of FIG. 26 being in temporal correlation. The arc voltage dips atthe beginnig of each current pulse because welding power is heldconstant. Because the current pulse causes oscillation of the weld pool,the initial dip in voltage is rapidly followed by an increase in voltageto above the steady state voltage present when the arc current is at itsbase level. The arc voltage attains its peak approximately at the sametime as the current terminates and thereafter the voltage gradually andcyclically decays back to its initial value prior to the pulse. Thegradual decay in the arc voltage is caused by the damping, primarily bygravity, of the cyclic oscillations induced in the weld pool by thecurrent pulse, and the cyclic changes in the arc voltage are caused bythe cyclic changes in arc length as the oscillating weld pool rises andfalls relative to the tip of the welding electrode. The fast part of thecyclic decay in arc voltage is used as a sampling time, in which arcvoltage is determined by the instant apparatus. Also shown in the lowerpart of FIG. 26 is the sampling interval, which is the interval requiredby the instant apparatus make one measurement of arc voltage. It will beseen that a large number of sampling intervals can be accommodatedwithin the sampling time. Following the sampling time there is aninterval designated "averaging and processing time", which is used bythe computer 734 (FIG. 19) for analysis of the arc voltage measurementstaken during the sampling time; if desired and necessary, the averagingand processing time may also be used by the computer to effectadjustments in base current and pulse current in order to maintain aconstant weld pool mass by maintaining a constant frequency ofoscillation. The pulse frequency should be adjusted so that, as shown inFIG. 26, the averaging and processing time is completed before the nextcurrent pulse occurs.

The uppermost part of FIG. 27 repeats the arc current/time graph in theupper part of FIG. 26 but shows only a single current pulse. The centerpart of FIG. 27 shows the corresponding arc voltage/time graph, butrepresents only the A.C. component of the arc voltage, which appears atthe outputs of the arc voltage AC coupler circuit shown in the lowerpart of FIG. 24. Also, as indicated by the short vertical lines in thesecond part of FIG. 27, the instant apparatus does not analyze thecontinuously-varying voltage, but rather samples the voltage at themid-point of regularly-spaced sampling intervals, 128 of which areaccommodated in each sampling time.

The lowermost part of FIG. 27 shows an averaged arc voltage which thecomputer produces by averaging the discrete values produced as justdescribed over a number of successive sampling times, this averagingbeing carried out by the algorithm shown in FIG. 28. It has been foundthat the instant apparatus produces sufficienty large amounts ofaberrant data that analysis of the "raw" voltage data obtained from thecurve shown in the central part of FIG. 27 may not give good results.Analysis of the averaged curve shown in the lowermost part of FIG. 27has been found to give much superior results.

FIG. 28 shows the algorithm used to produce the average curve shown inthe lowermost part of FIG. 27. When the ith digital voltage value (i.e.the voltage value for the ith sampling interval) of any sampling time isreceived by the computer, the previous average for the ith samplinginterval is multiplied by (N-1) where N is a constant set by theoperator using the software described below. The new voltage value isadded to this product, and the resultant sum divided by N to produce thenew average. It can be shown that this averaging process yields a waveform having a signal-to-noise ratio improved by a factor of (2N-1)⁰.5.

It might be thought that it would be more logical to derive frequencydata by averaging the last (say) 10 or so voltage values at each point.However, this method has the disadvantage of requiring extra storagespace and also requiring a greater amount of calculation to produce theaverage curve. Although it is also in theory possible to obtainfrequency data from the unaveraged curve shown in the central part ofFIG. 27, and then to average the frequency so produced over a number ofcycles, such a method would have the disadvantage that the finalcalculation of an average frequency would only occur after (say) everyfour or five sampling intervals, whereas the algorithm shown in FIG. 28permits adjustment of welding parameters after every pulse.

Although the algorithm shown in FIG. 28 gives good results understeady-state welding conditions, which were used in the tests describedbelow, this averaging method may give rise to difficulties if majorchanges occur in the welding parameters during a given run. In thesecircumstances, it may be necessary to use other averaging techniques,but it is believed that appropriate averaging techniques will readily beapparent to those skilled in the art.

FIG. 29 is an idealized flow diagram of the algorithm which is used formaintaining the mass of the weld pool constant despite variations inwelding conditions. As will be apparent from the more detaileddescription below, the various steps of the algorithm shown in FIG. 29are not carried out continuously but only at discrete intervals. Asshown in FIG. 29, the operator establishes an initial set point for thefrequency of oscillation of the weld pool which will produce the size ofweld pool believed to be optimum for a given welding operation. Thisinitial set point K₁ is put into the instant apparatus by the operator,who also establishes the other parameters using the potetiometercontrols previously described. These initial settings by the operatorestablish a base current I_(B). Upon a pulse command from the computer,this base current I_(B) is increased to the pulse current I_(P), whichcauses oscillations in the arc/weld pool system as previously described.Also as previously described, the resultant oscillations in the arc/weldpool system cause changes in the arc voltage, which is submitted to thearc voltage sampling/period calculation routine already discussed aboveto produce a measured period of oscillation, from which the actual weldpool mass K₂ can be calculated. The difference between the desired andactual weld pool masses is calculated, and a current correction I_(E)calculated and used to adjust the base current. The resultant frequencycalculation and base current is repeated at regular intervals after eachcurrent pulse. Updating can be frequent; for example, the preferredinstant apparatus described above with reference to FIGS. 19-25 has beenoperated with updating of the weld pool mass every 1/15 of a second,using a sampling interval of 160 microseconds and a totaling samplingtime of 15 milliseconds.

FIG. 30 shows the "weld joint preparation" 707 shown schematically inFIG. 19, together with the mount therefor. As already mentioned, forexperimental purposes the integer 707 was not a true weld jointpreparation but rather a single plate, thereby allowing a bead-on-plateweld to be performed. As shown in FIG. 30, the plate 707, which is madeof hot rolled mild steel, is mounted on a copper mount 802, which is inturn mounted on a hollow copper cooling block 804 provided with achannel through which a stream 806 of water can be passed for coolingpurposes. A thermal joint compound 808 is provided between the coppermount 802 and both the plate 707 and the cooling block 804 to ensuregood thermal contact. As will be apparent to those skilled in the art,in this apparatus the central region 801 of the plate 707 will bemaintained much cooler during welding than the remaining parts of theplate 707 because this sample region will be in good thermal contactwith the cooling block 804. Ordinarily, therefore, one would expect thatas a weld crosses region 801 on plate 707, the size of the weld poolwould decrease significantly because of the increase in the rate atwhich heat is removed from the weld pool. Accordingly, performing a weldin a straight line across region 801 provides a strenuous test of theability of the weld pool oscillation methods of the invention tomaintain a constant weld pool size despite major changes in weld poolconditions.

The improvement in maintaining constant weld pool size obtainable by theinstant weld pool oscillation methods when using the apparatus shown inFIGS. 19-30 as illustrated in FIGS. 31 and 32. FIG. 31 is a part of testdata taken using this apparatus but with the control system off so thata constant base current I_(B) is maintained, this being the normal priorart condition. As will be seen from FIG. 31, although the base currentremains constant, the period of oscillation, and thus the size of theweld pool, undergoes very substantial variations. In contrast, FIG. 32shows a similar plot using the same apparatus but with the controlsystem on so that base current is varied to maintain a constant weldpool size. It will be seen from FIG. 32 that substantial changes in basecurrent occur, but that the period of oscillation, and thus the mass ofthe weld pool, are maintained with much less variation than with theprior art illustrated in FIG. 31.

WELD POOL OSCILLATION METHOD SOFTWARE

The software used in the computer 734 to carry out measurement of weldpool oscillation is shown in FIGS. 33, 33A-33L and 34. As alreadymentioned, the computer 734 is a AIM-65 Rockwell computer used in thestandard configuration as received from the manufacturer. The softwareshown in FIGS. 33 and 33A-33G is stored in a single type 2716 EPROM inslot 225 of the computer's main board, and the software shown in FIGS.33H-33L is stored in a similar EPROM in slot 226 on the same board.

The control program shown in FIG. 34 is stored on magnetic tape and fedto the tape input of the computer 734, as described above with referenceto FIG. 20.

The tasks to be performed by the software include monitoring of operatorinputs from the pendant, control of the two translators, control of thewelding power supply and data collection and processing. The logic usedis that shown in FIG. 29. The initial values of base current, pulsecurrent, duration and frequency of pulses are set manually by theoperator and thereafter the base current is adjusted automatically bythe computer. The software also allows for an automatic voltage controlmode (handled by sub-routine AVC shown in FIG. 331), in which thecomputer samples the arc voltage and controls the Z-axis translator 716so as to keep this arc voltage within acceptable levels. The use of theautomatic voltage control is optional and this voltage control was notused in the tests described below.

The program MAIN 850 shown in FIG. 3 is the "home base" or "fall-backposition" for the computer. Basically, this program waits for the userto request a parameter change or for an interrupt to be received fromone of the interrupt timers associated with the various routinesdescribed below.

As already mentioned, several of the subroutines described below areassociated with interrupt timers. As those skilled in the art are aware,interrupt timers are devices which generate interrupt signals whichcause the computer to leave the routine it is previously executing andperform the routine specified by the associated interrupt timers. Eachtimer is loaded by the software with a time delay value ofpre-determined magnitude. Each interrupt timer generates its interruptsignal after the appropriate predetermined time delay value has passed.In the present case, the sub-routine INTHAN shown in FIG. 33C is used todetermine which interrupt signal has been received and thus whichtimer-associated sub-routine should be executed. After the routineassociated with the received interrupt signal has been performed, thecomputer returns to the same place in the program where it was beforethe interrupt signal was received and the interrupt timer is reset, sothat the same interrupt signal will not be generated again until after afurther appropriate delay period has elapsed. Thus, any one subroutinecannot be called too frequently, so that the computer has time toperform all the necessary tasks. Also, only one interrupt is serviced ata time, so that the computer will execute the appropriateinterrupt-associated sub-routine before returning to the previous task.Finally, the computer always returns to this program MAIN betweeninterrupt-associated subroutines. These interrupt-associated subroutinesinclude the pendant monitoring routine PEND shown in FIG. 33J and thepower supply pulsing routine PULSE shown in FIG. 33E. Subroutines START,STOP (both of which are shown in FIGS. 33D) and JOG (shown in FIG. 33L)are called from subroutine PEND shown in FIG. 33J, while subroutinesATOD (shown in FIG. 33F) and COMPUT (shown in FIG. 33H) can be calledfrom subroutine PULSE, as is the optional automatic voltage controlroutine AVC shown in FIG. 33I.

As already mentioned, program MAIN 850 shown in FIG. 33 is the "homebase" for the computer. When welding is not being performed, thecomputer remains in the program MAIN, except that the subroutine PENDinterrupt timer runs to enable the computer to scan theoperator-operated pendant and execute any button pushes thereon. Asshown on FIG. 33, the program MAIN 850 beings at block 852 by executingthe subroutine INIT, which is an initialization routine which isdescribe below with reference to FIG. 33A. Since block 852 is outsidethe loops in the program MAIN, it is only executed when the computerbegins operation, and is not repeated during any period of operation.Next, at 853 the interrupts are enabled, and the built-in screen on theAIM-65 computer is cleared. The program then proceeds, at block 854, tooutput the phrase "PUSH C TO CHANGE" on the built-in screen. After ashort delay provided to enable the user to respond, the program proceedsat block 856, to check whether the C key on the keyboard of the computerhas been pressed, this being the key which the operator presses when hewishes to enter a parameter change. If key C has not been pressed, theprogram loops back to the beginning of block 856 and thus waits at block56 until the C has been pressed, thereby waiting in a stand-by,non-operating condition until the operator proceeds to take action. Whenthe operator presses key C, the program proceeds to block 860, where thesubroutine USER is executed and, after return from subroutine USER, theprogram loops back to block 853.

Details of the subroutine INIT, referred to in block 852 of FIG. 33, areshown in FIG. 33A. From a beginning point at block 862, subroutine INITinitializes the analog/digital converter 726 (FIG. 20). Block 864actually sets the period for which a pulse is to be maintained, and theduration of the delay between successive pulses. The program thenproceeds, at block 865, to initialize the digital/analog converter 722(FIG. 20). Next, at block 866, the input/output unit 730A (FIG. 20) isinitialized, being loaded with initial values of various parameterscalculated by the operator. The second input/output unit 730B issimilarly initialized at block 868. At block 870 the computerinput/output module is initialized. Thereafter, default values areassigned to various parameters and flags at block 872. As will beapparent to those skilled in the art, setting of such default valuesensures that all required parameters always have some workable value,where no other value is provided by preceding operations. Then, at block874, an "interrupt vector" is initialized. This "interrupt vector" isactually an address specifying the beginning of the interrupt handlingsubroutine INTHAN, and block 874 thus ensures that thereafter, wheneveran interrupt is received, the program will jump to INTHAN. Next, atblock 875, the pendant interrupt timer is started. Finally, thesubroutine INIT is exited at block 876, and a return made to the programMAIN.

The full listing for subroutine INIT is given in the Appendix to thepresent description to the conventional Rockwell 6502. AssemblerLanguage. Also reproduced in this Appendix is the Labeling Routine whichsets initial values of various variables used by subroutine INIT.

The subroutine USER, mentioned in block 860 in FIG. 33 is shown in moredetail in FIG. 33B. As shown in FIG. 33B, subroutine USER proceeds froman entry point at block 878 to a block 880 where it displays on thecomputer display a message asking if the operator wishes to change theY-axis travel parameters. If the operator presses Y (yes), the programdisplays to the operator, at block 882, a message asking the operator toinput the Y-axis travel speed, then waits until the operator enters anappropriate response on the keyboard, and stores the response in anappropriate register. In an exactly similar manner, the program outputsmessages to the operator and receives and stores the Y-axis traveldirection at block 884, and the Y-axis distance at block 886. At block888, the programmer is advised by the operator whether he wishes to usethe autoreverse feature of the program. In the tests described below,the autoreverse feature was not used. The purpose of this feature is toallow the weld bead to reweld over the same path in the reversedirection, in order to determine whether there is any directionalaberration to the data achieved in the experimental apparatus.

From block 888, or from block 880 if the operator presses any key otherthan Y, the program proceeds, at block 890, to display a message askingthe operator whether he wishes to change the power supply parameters. Ifthe operator presses key Y, the program proceeds through blocks 892,894, 896 and 898 which, in a manner similar to that described above withregard to block 882, allow for inputs of "low pulse length" (i.e.spacing between successive current pulses in which the current is at thebase level) at block 892, "high pulse length" (i.e. pulse duration) atblock 894, "low pulse amplitude" (i.e. base current) at block 896 and"high pulse amplitude" (i.e. pulse current) at block 898.

From block 898, or if the operator presses any key other than Y at block890, the program proceeds, at block 900, to display a message asking theoperator if he wishes to change the automatic voltage control (AVC). Ifthe operator presses key Y, the program proceeds through blocks 902 and904, which are both generally similar to block 882 described above, andin which the AVC gain and the AVC dead-band respectively are set. TheAVC dead band sets the range within which variations in the arc voltagecan occur without causing movement of the torch. As will be apparent tothose skilled in the art, minor variations in the arc voltage isinevitable, and the presence of the dead-band is necessary ifunnecessary changes in arc length by the Z-axis translator 716, andpossible hunting is to be avoided.

From block 904, or if the operator presses any key other than Y at block900, the program proceeds to block 906, where it displays a messageasking the operator if he wishes to change data collection parameters.If the operator presses key Y, the program proceeds through blocks908-914, which are all generally similar to block 882 described above,and which allow for input of the location of a data table at block 908,sampling interval at block 910, number of samples to be taken duringeach sampling time (see description of FIG. 26 above) at block 912 andaverage weighting factor at block 914. The average weighting factorinput at at block 914 specifies the value of parameter N in thealgorithm shown in FIG. 28.

From block 914, or if the operator presses any key other than Y at block906, the program proceeds at 916, to display a message asking theoperator if he wishes to change JOG speeds i.e. the speed at which thetranslators 714 and 716 will move the welding torch 708 (FIG. 9) whenthe operator depresses the JOG buttons on the pendant. If the operatorpresses key Y, the program proceeds through blocks 918, 920 and 922,which are all generally similar to block 882 described above, and whichallow for inputs of X, Y and Z JOG speeds respectively. Obviously, block918 is superfluous in the apparatus shown in FIGS. 19-25, in which noX-translator is provided, but block 918 is included in the software toallow for future modifications.

From block 922, or if the operator presses any key other than Y at block918, the program proceeds, at block 925, to display a message asking theoperator if he wishes to change the parameters of the current controlprogram (shown in FIG. 34). If the operator presses key Y, th eprogramproceeds, at block 927, to ask the operator if he wants the currentcontrol program activated or not, and then, at blocks 929, 931 and 933,asks the operator to input the values of the set point STPNT, deadbandand gain parameters respectively, required by the current controlprogram.

From block 933, or if the operator presses any key other than Y at block925, the subroutine USER is exited at 924 back to MAIN.

All the parameters which are input to the computer during subroutineUSER must be pre-calculated by the operator and, where these parametersare numerical values, must be converted into hexadecimal notation sincethe AIM-65 computer will only accept numerical inputs in hexadecimalnotation. The Y-axis travel speed (YSPD) set at block 882 cannot exceedtwo inches per minute and the input to the computer is calculated by thefollowing equation:

    YSPD=15000×travel speed (inches per minute)

The 15,000 in this formula is in decimal notation. The Y-axis traveldirection (YDIR) input at block 884 can only be+or-(left or rightrespectively). The Y-axis distance (YDIS) input at block 886 is thedistance which the Y-axis translator 714 (FIG. 19) will move the weldingtorch during a welding operation and is input directly in inches, thepermissible range of values being 01 to 0F (1-15 in decimal notation).As previously mentioned, the autoreverse feature input block 888 was notin fact used, but is simply input as Y (yes) or N (no).

The low pulse length (low pulse delay, LOPD) input at block 892 and thehigh pulse length (high pulse delay HIPD) input at block 894 arecalculated from the following equation:

    LOPD/HIPD=delay time (seconds×10.sup.6)

In this formula, the 10⁶ is in decimal notation. The low pulse amplitude(base current, BASEI) input at block 896 and the high pulse amplitude(pulse current, PULSAMP) input at block 898 are calculated to thefollowing formula:

    BASEI/PULSEI=current (amperes)×10.23

In this formula, the 10.23 is in decimal notation. The value of PULSAMPto be input is the difference between the pulse and base currents, notthe absolute value of the pulse current.

The optimum value of the AVC gain (AVCSPD) input at 902 is not usuallyknown in advance, and accordingly an initial value is entered andadjusted based upon the operator's evaluation of welding performance.The value of AVCSPD can be zero or any hexadecimal number from 0400 toFFFF. Setting AVCSPD to 0 disables the AVC feature of the apparatus. Thevalue of the AVC dead band (AVCDB) to be input at block 904 is 33.3 timethe desired dead band value in volts.

The location of data table parameter (BASLOC) input at block 908determines the locations in the computer memory of a sample table andaverage sample table for any particular test. Permissible values of thisparameter are 0800 to 0E00 (in hexadecimal notation). The new data tableis stored at the memory location corresponding to the value input andthe average data table starts one memory page later. Thus, for example,if the input is 0E00 the first element of the new data table is locatedat address 0E00 and the first element of the average data table will belocated at 0F00. The value of the sampling interval (SAMPIN) input at910 is equal to the sampling interval in microseconds, while the numberof samples input at block 912 is simply equal to the number of samplesto be corrected; acceptable values range from 01 to FF (1-255 in decimalnotation). (That is to say the software will accept values from 1 to FF;however, since the software is designed to detect two maxima and twominima in the arc voltage, a number of samples less than 5 will notproduce any results and in practice a number of samples less than about20 will not produce useful results. It has been found that using 128samples generally gives good results. Similarly, the average waitingfactor (NSET) input at block 914 is equal to y where

    N=2.sup.Y ;

acceptable values of this parameter range from 1 to 5.

The X-axis and Z-axis jog speeds (XJGSPD and ZJGSPD respectively) inputat blocks 918 and 922 respectively, should be equal to 30000 (in decimalnotation) times the desired jog speed in inches per minute. The X-axisjog speed (XJGSPD) input at block 920 is calculated in substantially thesame manner but using a multiplier of 15000 rather than 30000.

Before the details of the remaining software shown in FIGS. 33C-33L aredescribed, it is necessary to outline the manner in which an operatorperforms the welding operation using the apparatus shown in FIGS. 19-25.Before initiating welding, the operator presses C on the keyboard andperforms the USER subroutine as already described to change any desiredwelding parameters. Thereafter, before initiating welding the operatormust position the torch in the correct position relative to the plate707 (FIGS. 19 and 30) using the Y-JOG and Z-JOG buttons on the pendant.Once the welding electrode is in the correct position, the operatorinitiates welding by pressing the weld start button on the pendant,thereby, in a manner to be described below, causing the computer toautomatically start welding using the touch/start method in which thewelding electrode 708 (FIG. 19) is lowered until it touches the workpiece and then withdrawn an appropriate distance, the arc being formedas the electrode is withdrawn. To stop the welding operation, theoperator simply presses the weld stop button on the pendant.

FIG. 33C shows the interrupt routine INTHAN, which is executed wheneveran interrupt is received and the execution of the approriate subroutine;subroutine INTHAN is necessary because the program MAIN cannotdistinguish between the various possible interrupt signals. From anentry point at block 926, subroutine INTHAN proceeds, at block 923, tostore the contents of the A, X and Y registers temporarily in order topreserve these for later processing. Next, at block 930, a flag ADIFR,relating to the analog/digital converter 726 (FIG. 20) is checked to seeif it is set. If the analog/digital converter interrupt ADIFR is set atblock 930, the program proceeds, at 932 to check a flag ADIER, which isset when one of the buttons on the operator pendant is pushed, ischecked, and if this flag is set, the program proceeds to block 936 andproceeds to execute subroutine PEND. (The two testing operations, blocks930 and 932, are necessary because there are two separate interrupttimers associated with the analog/digital unit 726, namely a pendanttimer which controls scanning of the pendant, and a sampling timer,which controls data collection. Receipt of an interrupt timer will causeblock 930 to produce a positive result. Accordingly, when block 930produces a positive result, block 932 is executed to determine whichinterrupt timer produced the interrupt. If it is the pendant timer,subroutine PEND must be executed as already described; if it is thesampling timer, subroutine ATOD must be executed, as described below.)If, however, at block 932 flag ADIER is not set, the program proceeds toblock 934, and executes subroutine ATOD from block 930, or if the flagADIFR is not found to be set at block 930, the program proceeds, atblock 938, to test whether a pulse timer interrupt has been received. Ifa pulse timer interrupt has been received, the program proceeds to block940 and executes subroutine PULSE. If no pulse timer interrupt has beenreceived, the program proceeds, at block 942, to test whether a distancecounter interrupt has been received. This distance counter indicateswhen the welding electrode has covered the Y-axis distance input atblock 886 (FIG. 33B). If a distance interrupt is found at block 942, theprogram proceeds to block 944 and executes a subroutine YDIST; thissubroutine YDIST basically deals with the (presently unused) autoreversefeature and merely makes appropriate arrangements for reversal ofwelding direction if the autoreverse feature is set. Otherwise, YDISTmerely stops the movement of the welding electrode. If no distancecounter interrupt is found at block 942, the program restores at block945, the original values of the A, X and Y registers and then exits viablock 948.

The next subroutine to be described will be the subroutine PEND shown inFIG. 33J. As previously mentioned, the pendant has the form of a 4×4matrix, in which each pushbutton interconnects one drive line and onesensing line. The subroutine PEND is called every 65 milliseconds. Toscan a row of the matrix of the pendant, the appropriate drive line isenergized and the sensing line checked. The optical isolators used inunits 718C and 718D (FIG. 20) have a relatively slow response time ofapproximately 4 milliseconds. Accordingly, it is only possible to checkone row of the pendant each time PEND is called, and the subroutine isarranged accordingly.

Selection of the row to be checked is controlled by a pendant flag,PENFLG set as described below. Accordingly, from a start point 1126,subroutine PEND proceeds immediately to block 1128, where it checks tosee whether PENFLG is equal to 0. If so, the program proceeds to resetPENFLG to 1 at block 1130, and then at block 1132, checks to see whetherany of the X, Y and Z-jog buttons in the first row have been pressed. Toperform this operation, the computer must energize pendant line 4 andcheck each of the pendant sensing lines, lines 0-3, for an input. Inpractice, because of the very slow response of the optical buffer, thedriving and sensing operations cannot both occur at block 1132,otherwise a delay of at least 4 milliseconds would have to be built intothe program at block 1132 and subroutine PEND would consume an excessiveamount of computer time. Accordingly, at block 1132 the computeractually energizes line 5 (the driving line for the second row), thenimmediately checks the sensing lines. Because of the delay in opticalisolators, the energization of line 5 has no immediate effect on thesensing lines, and the inputs from the sensing lines are determined bythe energization of pendant line 4, which was effected on the previouspass through subroutine PEND, during the checking of the third row asdescribed below. Also, operation 1132 is somewhat more complicated thanwould appear from FIG. 33J since, for scanning purposes the directionbuttons is part of the first row, but mere change in the directionbutton without any other button presses does not require calling ofsubroutine JOG. Accordingly, block 1132 first checks whether any buttonshave been pushed in the first row and then checks whether the buttonpushed is the X, Y or Z-jog buttons actually results in the calling ofsubroutine JOG. If at block 1132, the sensing line inputs indicate thata button in the first row has been pressed, the program proceeds viablock 1134 to the subroutine JOG shown in FIG. 33L. If at block 1132 itis determined that no buttons have been pressed, the program proceeds toblock 1138 and restores the original contents of the A, X and Yregisters (which were saved at block 928 (FIG. 33C) in subroutineINTHAN). Although not shown in FIG. 33K, block 1138 also restarts thependant timer.

For experimental and testing purposes, it is convenient to have somemethod for physically removing the weld pool from the weld jointpreparation so that the recess in the weld joint preparation thusproduced can be measured to determine directly weld pool size and weldpenetration. This feature can conveniently be provided by arranging forthe software to control the operation of the gas solenoid (describedabove with reference to FIG. 19), and adding an appropriate subroutinebetween blocks 1152 and 1154 to cause a violent blast of gas to issuefrom the gas solenoid, thereby blowing the weld pool from the weld jointpreparation.

If at block 1128 it is determined that PENFLG is not equal to 0,subroutine PEND proceeds to block 1142 and checks if PENFLG is equalto 1. If so, PENFLG is reset to 2 at block 1144 and then, at block 1146,the pendant is checked to see if the only button in the second row,namely the weld start button, has been pressed. For the same reason asexplained above with reference to block 1132, at block 1146, it isactually pendant line 6 (the drive line for the third row which isenergized and thereafter pendant line 3 (the fourth sensing line) ischecked to see if the energization of pendant line 5 effected at block1132 in the previous pass through subroutine PEND resulted, because ofpressing of the weld start button, in a signal on pendant line 3. If thestart button has been pressed, the program proceeds via block 1142 tothe subroutine START shown in FIG. 33B. If the start button has not beenpressed, the program proceeds from block 1146 through blocks 1138 and1140 previously described.

Finally, if at block 1142 it is determined that PENFLG is not equal to1, the third row of the pendant, which contains only the weld stopbutton must be checked. Accordingly, the program proceeds at 1150 to setPENFLG equal to 0 and then at block 1152, checks whether the stop buttonhas been pressed. For the same reasons as explained above in relation toblock 1132, at block 1152 the program actually energizes pendant line 4(the drive line for the JOG row) and then immediately checks pendantline 3 for a signal caused by the energization of pendant line 6 atblock 1146 in the previous pass through subroutine PEND. If at block1152 it is determined that the stop button has been pressed, thesubroutine proceeds via block 1154 to subroutine STOP shown in FIG. 33B.On the other hand, if at block 1152 it is determined that the stopbutton has not been pressed, the subroutine proceeds via blocks 1138 and1140 described above.

The subroutine PULSE mentioned in block 940 in FIG. 33C will now bedescribed in detail with reference to FIG. 33E. Subroutine PULSEcontrols the pulsing of the arc current in accordance with theparameters previously set by the operator (see description of blocks890-898 given above with reference to FIG. 33B. From a start point atblock 1002, subroutine PULSE proceeds at block 1004 to check the valueof a pulse flag PFLG. This flag is provided to provide proper switchingbetween the base and pulse currents. As already described with referenceto FIG. 33C, subroutine PULSE is called whenever a pulse timer interruptis received. The manner in which the pulse timer is loaded will bedescribed below, but it should be noted that subroutine PULSE is calledwhen either a negative or positive transition in current is requiredi.e. at the beginning and end of each pulse. Accordingly, subroutinePULSE proceeds from a start point at block 1002 to a block 1004 where apulse flag PFLG is tested to see whether it has a value 0 or 1. If thepulse flag is low, a negative transition in the current level isrequired, and this is handled by the remaining block in the right-handcolumn of FIG. 33E. On the other hand, if the pulse flag is high apositive transition in the current level is required, and this operationis handled by the blocks in the left-hand column of FIG. 33E.

If at block 1004, the pulse flag is found to be high, the programproceeds at block 1006 to set the pulse flag low and to read the DCcoupled arc voltages. After the DC coupled arc voltage has been read,block 1006 switches the analog/digital converter 726 (FIGS. 19 and 20)so that it converts the A.C. coupled output from the circuit shown inthe lower part of FIG. 24 rather than the DC coupled output from thecircuit shown in the upper part of that Figure. As those skilled in theart are aware, the Gordos AD-10 circuit board used as the analog/digitalconverter unit 726, although having several input channels, only effectsconversion of any one of these channels at any one time. Accordingly,the switching at block 1006 is required to set the converter 726 so thatit will thereafter supply to the computer a digital signal representingthe DC coupled arc voltage. Then, at block 1008, the program tests tosee whether the AVC gain is equal to 0. If the AVC gain is not equal to0, the program proceeds to block 1010 and executes subroutine AVC shownin FIG. 33I. Upon return from AVC, or if the AVC gain is found to be 0at block 1008 (indicating that the operator does not wish the AVC gainfeature to be used), the program proceeds to block 1012, where thecurrent is set to the pulse current value, the value of HIPD (the highpulse delay indicating the duration of the pulse) is loaded into thepulse timer and the pulse timer is restarted. Thereafter, the programproceeds at block 1014, to restore the original contents of the A, X andY registers (which were saved at block 928 in FIG. 33C) and then exitsvia block 1016.

If, on the other hand at block 1004 the pulse flag is found to be low,this pulse flag is reset to high at block 1018, the value of LOPD (thelow pulse delay, indicating the gap between pulses) is loaded into thepulse timer and the pulse timer restarted at block 1020 and thereafterblocks 1022 and 1024 terminate the pulse current and restore the currentto its base value. Next, at block 1026, the sampling interval (set bythe operator at block 910, as described above with reference to FIG.33B) is tested to see it is is equal to 0. If the sampling interval isnot equal to 0, the subroutine ATOD is executed at block 1028 andimmediately thereafter the subroutine COMPUT is executed at block 1030.The contents of the A, X and Y registers are then restored at block 1032(these registers having been saved at block 928 in FIG. 33C) andsubroutine PULSE is exited at block 1034. If at block 1026 it is foundthat the sampling interval is equal to 0 (which indicates that theoperator does not wish voltage sampling to be effected), the programproceeds directly from block 1026 to block 1032 and then exits via block1034 as previously described.

The subroutine JOG, which is called via block 1134 in subroutine PEND(see above description of FIG. 33J) is shown in FIG. 33L.

From a starting point at block 1212, subroutine JOG proceeds, at block1213, to save the value of the direction switch. Next, at block 1214,the subroutine tests to see whether it is the Z-JOG button which hasbeen pushed. It should be noted that block 1214 is not analogous toblock 1132 in FIG. 33J; since it has already been established that oneof the buttons in the first row has been pushed, it is only necesary foroperation 1214 to check whether the sensing line on which the Z-jogbutton is located is producing an appropriate response. If at block1214, it is found that the Z-jog button has been pushed, the programproceeds, as indicated by I--I in FIG. 33L, to a block 1266 to bedescribed below. If at 1214 it is found that the Z-jog button has notbeen pushed, the program proceeds, at block 1216, to check whether theY-jog button has been pushed. If not, the interrupt was from the X-jogbutton and accordingly, block 1218 the program tests whether the X-axismotor is switched on. If so, a X flag, XFLG is set to the value 0 atblock 1220; if not, the same flag is set to the value 1 at block 1221.From block 1220 or block 1221, the program proceeds, at block 1222, tocheck whether the direction switch is closed (as described above, thisdirection was saved at block 1213). If the direction switch is closed,the chosen direction is right, set at block 1224; if not, the directionis left, set at block 1226. After executing either block 1224 or 1226,the X-axis motor is started at block 1228.

Once the motor has been started, the program proceeds at block 1230, totest whether the X-jog button is still pushed and, so long as thisbutton is still pushed, the program merely loops through block 30,allowing continuous motion by the X-axis motor. When the X-axis jobbutton is released, the program proceeds, at block 1232, to checkwhether the X flag, XFLG is set. If the X flag was not set i.e.=0,thereby indicating that the X-axis motor was switched off at block 1218,the X-axis motor is switched off at block 1234, whereas if the X flag isset indicating that the X-axis motor was on at block 1218, the programproceeds from block 1232 to block 1236, where the X-axis motor is allowsto reume its former speed and direction. From block 1234 to 1236, theprogram proceeds at block 1238, to restore the original contents of theA, X, Y registers (saved at block 928 in FIG. 33C) and is exited viablock 1240.

It will be appreciated that since no X-axis motor is actually used inthe present form of the apparatus, blocks 1218-1240 are presentlysuperfluous but are provided in case it should be desired to provide anX-axis translator in the apparatus.

If at block 1216, it is found that the Y-jog button has been pushed, theprogram proceeds from block 1216 to a block 1242, which is the beginningof a sequence of blocks 1242-1264, which are Y-axis blocks exactlyparallel to the X-axis blocks 1218-140 described above. Accordingly,blocks 1242-1264 will not be further described.

As mentioned above, if at block 1214 it is found that the Z-jog buttonhas been pushed, the program proceeds, as indicated by I--I in FIG. 33L,to block 1266, which is the first of a sequence of blocks 1266-1282which handle the Z-axis motor. However, the sequence of block for theZ-axis motor is somewhat different from those for the X- and Y-axismotors, since the Z-axis motor is not operated during welding (exceptfor automatic operation by the subroutine AVC), and thus there is noneed to save and restore original settings of the Z-axis motor in thesame way that blocks 1218, 1220, 1221, 1232, 1234 and 1236 save andrestore the original settings of the X-axis motor. Accordingly, block1266 is not equivalent to blocks 1218 and 1242, but is instead adirection switch testing operation exactly similar to blocks 1222 and1246. Block 1266 begins a sequence of blocks 1266, 1268, 1270, 1272 and1274 which are exactly parallel to the sequence of blocks 1222-1230respectively associated with the X-axis. When the Z-jog button isreleased, the program leaves block 1274 and proceeds at blocks 1276 toshut off the Z-axis motor. Next, at block 1278, the set point voltage isobtained for the subroutine AVC. Also at block 1278, a flag VLTFLG isset equal to 1 for purposes to be described below. Thereafter, theprogram executes blocks 1280 and 1282 which are exactly parallel toblocks 1238 and blocks 1240 respectively described above.

The subroutines START and STOP mentioned in blocks 1148 and 1154respectively in subroutine PEND (FIG. 33J) will now be described withreference to FIG. 33D. As already mentioned, the subroutines START andSTOP are called via subroutine PEND when the operator presses the weldstart and weld stop buttons respectively on the pendant.

The starting point of subroutine START is designed 950 in FIG. 33D. Thefirst step in subroutine START is omitted from FIG. 33D for the sake ofconvenience; this initial step checks whether an arc status registerindicates that an arc is already present, thus indicating that theoperator has pushed the start weld button by mistake. If the arc isalready pressed, the subroutine START is exited. If the initialoperation indicates that an arc is not present, the program proceeds, atline 952, to turn on the gas and water solenoids (via isolation unit718--see FIG. 19) and then at block 954, causes the control module 704(FIG. 19) to set a starting weld current level. This starting weldcurrent level is set in the initialization routine of the apparatus andis not set by the operator in the subroutine USER described above, sincethe optimum starting current level is fixed for a given apparatus and itis unnecessary to reset it before every run. Next, at block 956, thepower supply contractor again via unit 718 in FIG. 19. The program thenproceeds, at block 958, to test whether the DC coupled arc voltageindicates an open circuit i.e. whether any arc has in fact beenestablished. If the arc voltage at block 958 indicates that there is noopen circuit, so that an arc has already been established, the programproceeds to a block 978 described below. Normally, however, at block 958it will be found that there is an open circuit, indicated by an arcvoltage of approximately 70 volts, and accordingly, the programproceeds, at block 960, to operate the Z-axis motor so as to lower thewelding electrode 708 towards the plate 707. Once the lower of thewelding electrode has begun, the DC coupled arc voltage is tested atblock 962, the program looping through block 962 until the arc voltagedrops almost to 0, indicating the establishment of an arc; as thoseskilled in the art are aware, such an arc will only be established whenthe electrode 708 is touching or almost touching the plate 707. Once thearc is established, the program waits at block 964 for a predeterminedperiod; this delay is desirable because the operations of the computersoftware are so fast that it is desirable to allow the arc to stabilizebefore the computer takes any further action. The program then proceedsto begin driving the Z-axis motor in the opposed direction at block 966,passing through a predetermined delay at block 968 and stopping themovement of the electrode at a block 970, thereby raising the electrode708 and establishing a proper gap between the electrode 708 and theplate 707 for the welding operation. Thus, blocks 952-970 automaticallyestablish the welding arc by the touch-start method. (Obviously, if thesolenoids and the contactor are operator controlled, blocks 952, 956,960, 962, 964, 966, 968 and 970 can be omitted.) The program thenproceeds, at block 972, to set the weld current to the base value, andto load the pulse timer (the same pulse timer used in subroutine PULSEdescribed above with reference to FIG. 33E) with the low pulse delayLOOPD and the the start of the pulse timer. Next, at block 974, a flagVLTFLG is set equal to 1, and a flag FRST equal to 0; as described belowwith reference to FIG. 33H, flag FRST is needed by the subroutine AVERGto advise it that welding has just started, so that the next set of datato be received will be the first data set of a weld run, while flagVLTFLG is required by subroutine AVC, as described below. Next, at block976, the computer energizes the Y-axis motor to cause movement of thewelding electrode parallel to the Y-axis, thereby beginning thebead-on-plate welding operation. Finally, from block 976, or from the NOexit of block 958, the program proceeds to restore the original valuesof the A, X and Y registers (which were saved at block 928 at FIG. 33C),and the subroutine START is finally exited via block 980.

The subroutine STOP is also shown in FIG. 33D is straightforward. Whenthe operator presses the weld stop button on the pendant, subroutineSTOP is called via subroutine PEND described above. From a startingpoint at block 982, the program proceeds to stop all timers at block984, to set the weld current to 0 at block 988 and to turn off the powersupply contactor at block 988. The program waits at a delay block 990 ofpredetermined duration, this delay allowing the arc to completely ceasebefore the gas and water solenoids are shut off at block 992.(Obviously, if the solenoids and the contactor are operator-controlled,blocks 988 and 992 are omitted.) Next, at block 994 a stack pointer isresent. Finally, all interrupt registers are cleared at block 996 and atblock 998 the pendant interrupt timer is restarted (it will be recalledthat the operator can of course use the pendant buttons when welding isnot in progress, although all the other interrupt timers are disabledwhen welding is not proceeding), and then, at block 1000, subroutineSTOP is exited to program MAIN, block 854.

The subroutine ATOD mentioned in block 934 of subroutine INTHAN shown inFIG. 33C, and in block 1028 of subroutine PULSE shown in FIG. 33E, willnow be described with reference to FIG. 33F. By comparing FIGS. 26 and33F, it will be seen that subroutine ATOD is called by subroutine PULSEimmediately after a restoration of welding current from the pulsecurrent level to the base current level and thus at the beginning of thesampling time shown in FIG. 26. This ensures that any ith voltage valuedetermined by ATOD is always taken at the same interval after thenegative transition of the weld current. Subroutine ATOD performssampling of the arc voltage during the cyclic decay of the arc voltagewith the damped oscillations of the weld pool, as described above withreference to FIG. 26.

From a starting point at block 1036, subroutine ATOD proceeds, at block1038, to clear the timer interrupt flags, thereby enabling furtherinterrupts to be received. In fact block 1038 clears an interruptdisable flag which was previously blocking other interrupts. Next, atblock 1040, a sampling timer, which is responsible for timing thesampling intervals referred to above with reference to FIG. 26, isloaded with the value of the sampling interval set at block 9 line 10 insubroutine USER (FIG. 33B) and then, at block 1042, the program proceedsto repeated testing of the value in the sampling timer, looping throughblock 1042 until the sampling interval has elapsed, and then proceedingfrom block 1042 to a block 1044 where the AC coupled arc voltage (fromthe arc voltage AC coupled circuit shown in the lower part of FIG. 24)is read. From this arc voltage is added at block 1046 an arbitraryoffset arc voltage, which allows all the voltage values to be recordedas positive numbers to simplify later handling. The arc voltage plusoffset calculated at block 1046 is then, at block 1048, stored inDATA(I), position I of a table DATA. On the first pass through block1048 I is equal to 0, this setting being effected at block 1056described below. Next, at block 1050, the value AVG(I) is output to anoscilloscope. As will be described below in connection with subroutineAVERG shown in FIG. 33H, AVG(I) is the averaged arc voltage shown in thelowermost part of FIG. 27 for the sampling point number I for which theoffsetcorrected arc voltage has just been placed in DATA(I). Moreover,since AVG(I) is calculated during subroutine COMPUT by means ofsubroutine AVERG, and subroutine COMPUT is only called at block 1030 ofsubroutine PULSE (see FIG. 33E) immediately following the calling ofsubroutine ATOD at block 1028, the value of AVG(I) output at block 1050is the value of this average calculated by COMPUT and AVERG followingthe previous sampling interval i.e. the oscilloscope display runs onecomplete pulse interval behind real time. It will be appreciated thatthe average output at block 1050 is actually in digital form and has tobe converted to analog form by the digital/analog converter 722 (FIG.19) before being sent to the oscilloscope. Block 1050 is also providedto means to place a marker or cursor at the minima and maxima located bysubroutine COMPUT so that the operator can check visually that thesoftware is locating the correct maxima and minima.

Following block 1050, I is incremented by 1 at block 1052 and is thentested at block 1054 to see if it is equal to NSAMP, the number ofsamples to be taken during the sampling interval, this number previouslyhaving been set by the operator at block 912 in subroutine USER (FIG.33B). If at block 1054I is not equal to NSAMP, the sampling time (seeFIG. 26) has not ended and further voltage samples must be collected.Accordingly, the program loops back from block 1054 to block 1041. If,however, I is equal to NSAMP at block 1054, the sampling time iscompleted, and I is set equal to 0 at block 1056 so that, when ATOD isnext called, on the first pass through block 1040 the offset-correctedare voltage will be placed in DATA(0), and all values in DATA will beplaced in the correct locations. The sampling timer is then stopped atblock 1050 and next at block 1060, the analog/digital converter 726(FIGS. 19 and 20) is switched so that it converts the DC coupled outputfrom the voltage isolation circuit shown in the upper part of FIG. 24rather than the AC coupled output from the arc voltage AC couplercircuit shown in the lower part of FIG. 24. This switching of theanalog/digital converter inputs is necessary because the subroutine ATODworks on the AC coupled arc voltage, whereas the subroutine PULSE, block1006 (FIG. 33E) requires the DC coupled arc voltage. Finally, subroutineATOD is exited via block 1062 back to subroutine PULSE.

The subroutine COMPUT and AVERG will now be described with reference toFIGS. 33K and 33H respectively; as may be seen from FIG. 33K, thesubroutine AVERG is actually called by subroutine COMPUT and in order tounderstand the process carried out by subroutine COMPUT it is necessaryto first describe the averaging process carried out by subroutine AVERG.

As shown in FIG. 33K, the subroutine COMPUT proceeds from a start pointat block 1156 to block 1157 where subroutine AVERG is called. As shownin FIG. 33H, subroutine AVERG proceeds from a start point at block 1076to block 1078 where it tests whether the values which have just beenplaced in table DATA by subroutine ATOD are the first data set of a weldrun; this test is accomplished by testing whether the flag FRST(previously) set at block 974 in routine START (FIG. 33D) is equal to 0.If FRST is equal to zero, and thus the table DATA contains the firstdata set for weld run, the program proceeds from block 1078 to block1092, where a counter I is set equal to 0. Then, at block 1094, AVG(I),the ith position in the average arc voltage table AVG referred to aboveat block 1050 in subroutine ATOD (FIG. 33F) is set equal to DATA(I).Next, the value of I is incremented at block 1096 and tested at block1098 to see if it is equal to NSAMP, the number of samples, andtherefore, the number of positions in DATA and AVG. If at block 1098 Iis not equal to NSAMP, the program loops back to 1094. As will beapparent to those skilled in the art, the program will pass throughblocks 1094, 1096 and 1098 NSAMP times, and will thereby transfer allNSAMP values in DATA to the corresponding locations in AVG. Finally, onthe NSAMPth pass through block 1098, I will be equal to NSAMP and theprogram will be leave block 1098 set FRST equal to 1 at block 1099 andexit back to COMPUT via block 1100.

If, however, at block 1078 VLTFLG is not set, and thus the data in DATArelate to a second or later set of a weld run, subroutine AVERG mustcarry out the averaging process the logic of which is shown in FIG. 28.Accordingly, the program proceeds from block 1078 to block 1080 where Iis again set equal to 0. Thereafter, at block 1082 the "old average" inAVG(I) is multiplied by (N-1), where N is the average weighting factor,as explained above with reference to FIG. 28. The resultant multipliedvalue in AVG(I) is then, at block 1094, increased by DATA(I) and the sumdivided by N at block 1086 to produce the "new" value of AVG (I).Following block 1086, the program proceeds to blocks 1088 and 1090,which are exactly parallel to blocks 1096 and 1098 respectivelydescribed above, and which serve to ensure that the program passesthrough blocks 1082-1086 NSAMP times, thereby calculating new values forall the NSAMP positions in AVG. When all the new AVG values have beencalculated, subroutine AVERG is exited via blocks 1009 and 1100, and theprogram returns to the exit of block 1157 in COMPUT (FIG. 33K).

Following the return from subroutine AVERG, the main portion ofsubroutine COMPUT is used to determine the oscillation frequency of theweld pool by searching for maxima and minima in the averaged arc voltagecurve. To avoid excessive consumption of computer time, subroutineCOMPUT locates only the first two maxima and minima. Subroutine COMPUTalso incorporates checks to ensure that small aberrations in theaveraged arc voltage curve which may produce temporary false changes inthe sign of the gradient of the curve are not recorded as true maximaand minima.

Upon return from subroutine AVERG at the exit from block 1157, thecounter I is reset to 0 at block 1158 and then incremented by 1 at block1160. (FIG. 33K shows a slightly idealized form of the routine COMPUT inwhich the search for the minimma and maxima is begun with the firstpoint on the averaged arc voltage curve. In practice, it is probablyunwise to begin with this first point, since transient effectsassociated with the negative transition in the weld current may tend toproduce false maxima and minima during the first few readings.Accordingly, at block 1158 I may be set to a small positive integerrather than 0. With a 140 millisecond sampling interval, it has beenfound convenient to begin the search for minima and maxima by setting Iequal to 10 (hexadecimal) at block 1158. However, the number to which Iis set at block 1158 should not exceed NSAMP/2, since otherwise it maynot be possible to locate two maxima and minima.) Following theincrementing of I at block 1160, block 1162 tests whether AVG(I) isgreater than AVG(I+1) i.e. whether the slope of the average voltagecurve is negative. Because the first true change of direction in theaverage arc voltage curve is a minimum (see the last graph in FIG. 27)if at block 1162 the slope is not negative it is necessary to follow thecurve until a negative portion is obtained. Accordingly, if at block1162 the slope is not found to be negative, the block loops back to 1160and continues to loop through block 1160 and 1162 until a descendingportion of the average arc voltage curve is located. When such adescending portion of the curve is located, the program proceeds from1162 to block 1164 where I is again incremented and then again to block1166 which is identical to block 1162 and again tests for negative slopeof the curve. If the slope of the curve is still found to be negative atblock 166, the program loops back to 1164. Thus, the program willcontinue to loop through blocks 1164 and 1166 until block 1166 indicatesthat the slope of the curve is no longer negative, thereby indicatingthat a potential minimum has been located. Once this potential minimumhas been located, the program proceeds, at block 1168, to test whetherthe voltage at the potential minimum is greater than the voltage at thethird succeeding point. If at block 1168 it is found that the arcvoltage at the potential minimum is greater than the arc voltage at thethird succeeding point, this indicates that the potential minimum is infact spurious since with the sampling intervals used with experimentalwork of about 140 milliseconds, it is not possible to proceed from atrue minimum to a true maximum and back to a lower value in threesampling intervals. Accordingly, if block 1168 gives a positive result,I is incremented by 3 at block 1170 and the program loops back to block1166, thereby resuming the search for a true minimum on the far side ofthe aberration. If, however, at block 1168 gives a negative result, thepotential minimum is accepted as a true minimum and the program proceedsat block 1172, to copy the value of I into a first minimum locationregister LCMIN1 and to copy the appropriate averaged arc voltage valuefrom AVG(I) into a first minimum voltage register, MIN1.

Since the location of the first minimum has now been located, theprogram proceeds to locate the first maximum. Firstly, at block 1174, Iis again incremented by 1 and then at block 1176 AVG(I) is tested to seeif it is less than AVG(I+1) i.e. whether the curve has a positive slops.Since the first minimum has now been passed, initially the curve willhave a positive slope and block 1176 will give a positive result,causing the program to loop back to block 1174. Accordingly, so long asthe slope of the curve remains positive, the program will simply loopthrough blocks 1174 and 1176. However, when a point is reached at whichthe slope of the curve is no longer positive, this constitutes apotential first maximum and the program proceeds from block 1176 toblock 1178, which is identical to block 1168 described above and testswhether the value of the curve at the potential maximum is greater thanat the third succeeding sampling point, as would be the case for truemaximum. If block 1178 yields a negative result, indicating that thepotential maximum is in fact merely an aberration, the program proceedsto increment I by 3 at block 1180 and then loops back to block 1176 toresume the search for a true maximum. If block 1178 gives a positiveresult, indicating a true maximum, the program proceeds at block 1182,to determine if the value of the curve at the potential maximum isgreater than MIN+3, MIN being the value of the curve of the previouslminimum stored at block 1172. Block 1182 acts to screen potential maximaby testing whether the voltage at the potential maxima differs from thatof the potential minimum by at least 30 mV. Empirically, it has beenfound that if this condition is not satisfied the potential maximum willbe due to an aberration. If block 1182 gives a negative result, theprogram loops back to block 1174 and resumes the search for a truemaximum. If, however, block 1182 gives a true result, the programproceeds, at block 1184, to copy I, which now represents the location ofthe first maxima into a first maximum location register LCMAX1, and tocopy the corresponding value of the curve into register MAX.

The program then proceeds, as indicated by G--G in FIG. 33K, to a seriesof blocks 1186, 1188, 1190 and 1192, which are exactly parallel toblocks 1164, 1166, 1168 and 1170 respectively previously described,accept of course that they locate the second minimum rather than thefirst. However, if block 1190 yields a positive result, the programproceeds to a further testing block 1194, which is exactly analogous toblock 1182 previously described but tests whether the value of the curveat the potential second minimum differs from the value of the curve atthe previous maxima by at least 30 millivolts. If not, the program loopsback to block 1186. If block 1194 yields a positive result, at block1196 the location of the second mimimum is copies into register LCMIN2and the corresponding minimum value of the curve copies into MIN.

The program then proceeds to locate the second maximum using a series ofblocks 1198, 1200, 1202, 1204 and 1206 which are exactly analogous toblocks 1174, 1176, 1178, 1180 and 1182 respectively previously describedand function in exactly the same manner. When block 1206 produces apositive result, the position of the second maxima is written intoregister LCMAX2 at block 1208.

The actual period of oscillation, PERD, is calculated by block 1209,which follows block 1208. Since the difference between the locations ofthe first and second maxima should constitute one period, and thelocations between the first and second minima should also equal oneperiod, the best value of the period is obtained by averaing these twodifferences i.e.

    PERD=[(LCMAX2-LCMAX1)+(LCMIN2-LCMIN1)]/2

which is the formulae applied at block 1209.

Subroutine COMPUT has been simplified in FIG. 33K for purposes ofillustration. The form of COMPUT shown in FIG. 33K represents thesubroutine actually carried out when the subroutine COMPUT is able tolocte two maxima and two minima i.e. when a "proper" set of data isreceived. To allow for cases where less than two maxima and two minimaare found, subroutine COMPUT makes use of a counter CYCNT. CYCNT is setequal to zero between blocks 1156 and 1157, and at the same point the"old" values of LCMIN1, LCMIN2, LCMAX1 and LCMAX2 from the previous passthrough subroutine COMPUT are saved in temporary storage registers. Eachtime a true maximum or minimum is detected (i.e. at blocks 1172, 1184,1196 and 1208) CYCNT is incremented by 1. Between blocks 1208 and 1209,the value of CYCNT is tested. If CYCNT=4, all the desired minima andmaxima have been detected and block 1209 is effected in the form shownin FIG. 33K. If CYCNT is not equal to 4, the operations performed are asfollows:

(a) CYCNT=0; no tru minima or maxima have been detected, so the "saved"old values of LCMIN1, LCMIN2, LCMAX1 and LCMAX2 are restored to theseregisters, then block 1209 is performed as written, thereby keeping theindicated period unchanged.

(b) CYCNT=1; only one true minimum has been detected and PERD is setequal to 2×LCMIN1;

(c) CYCNT=2; one true minimum and one true maximum have been detectedand PERD is set equal to 2×(LCMAX1-LCMIN1);

(d) CYCNT=3; two true minima and one true maximum have been detected andPERD is set equal to (LCMIN2-LCMAX1)+0.5(LCMIN2-LCMIN1).

In addition to calculating PERD, block 1209 also outputs the value ofperd to channel 3 of the digital/analog converter 722 (FIG. 20) fortransmission to the oscilloscope or other recording device.

The last of the subroutines shown in FIGS. 33-33L to be described in thesubroutine AVC shown in FIG. 33I. As previously mentioned, subroutineAVC is called by block 1010 in subroutine PULSE (FIG. 33E) and is thuseffected immediately before each positive transition in the weld currentafter the arc voltage has resumed its original, steady-state value whichit assumes during a steady base current. Accordingly, AVC adjustmentonly occurs once per pulse, shortly before the beginning of each pulse.This placement of subroutine AVC prevents the subroutine interferingwith the detection of the variations in arc voltage caused by weld pooloscillation, and also prevents the voltage set by subroutine AVC frombeing disturbed by the variations on arc voltage caused by the currentpulses.

As shown in FIG. 33I, subroutine AVC commences at a start point 1102.Although not shown in FIG. 33I, the first operation in subroutine AVC isto read the AVC gain parameter which has been set by the operator atblock 902 in subroutine USER (FIG. 33B). If this AVC gain is equal to 0,the AVC feature of the apparatus is disabled and accordingly subroutineAVC is immediately exited.

If the AVC gain parameter is not equal to 0, subroutine AVC proceeds, atblock 1104, to read the AC coupled arc voltage V and then, at block1106, tests to see whether the flag VLTFLG is set. As previouslymentioned, flag VLTFLG is set equal to I either by block 974 ofsubroutine START (FIG. 33D) or by block 1278 of subroutine JOG (FIG.33Lc). Thus, this flag is set at the beginning of each welding run or oneach occasion when the operator adjusts the vertical loction of thewelding electrode 708 (FIG. 19); either of these occurrencesnecessitates a resetting of the reference arc voltage V(COMMAND), andaccordingly if block 1106 produces a positive result, V(COMMAND) isreset equal to the arc voltage (previously read at block 1104) at block1107. Although not shown in FIG. 33I, block 1107 also resets VLTFLGequal to zero. From block 1107, subroutine AVC is immediately exited viablock 1124.

If, however, at block 1106 it is found that flag VLTFLG is not set, thisindicates that at least one previous pass through subroutine AVC hasoccurred since the beginning of the last weld run or the Z-axis movementof the electrode 708, and thus comparison of the actual arc voltage withthe reference arc voltage is required, with adjustment of the Z-axisposition of the electrode 708 if the difference between the actual andreference value of the arc voltage exceeds the arc voltage deadband (setby the operator at block 904 in subroutine USER--see FIG. 33B).Accordingly, if block 1106 produces a negative result the programproceeds, at block 1108, to calculate the difference between thereference arc voltage and the actual arc voltage, and then tests, atblock 1110, whether this difference is negative. If the difference ispositive, the Z-axis direction is set to up at block 1112; if thedifference is negative, the Z-axis direction is set to down at block1114 and then the sign of the difference is reversed at 1116, since thesucceeding operations require a positive difference (or error).

From block 1112 or 1116, the program proceeds, at block 1118, to testwhether the error is less than the deadband value. If the error is lessthan the deadband, the Z-axis motor is shut off at block 1120, and thesubroutine AVC is then exited via block 1124. If, however, at block 1118the error is found to be greater than the deadband, the programproceeds, at block 1122, to calculate an appropriate speed for theZ-axis motor, and then the Z-axis motor is started at block 1123. Block1122 is provided to prevent unnecessary hunting on the Z-axis, such asmight occur if a constant Z-axis motor speed were employed to correcterrors in arc voltage. The motor speed calculated at 1122 should besufficient to change the arc length so as to correct the arc voltageerror before the next pass through subroutine AVC multiplied by someconstant not greater than one. In practice, block 1122 multiplies theerror by a constant which is set empirically for a particular apparatus.From block 1123, subroutine AVC is exited via block 1124.

As previously mentioned, FIG. 34 shows the program fed to the tape inputof the computer, this program serving to carry out adjustment of thewelding current by the logic shown in FIG. 29. The program begins, atblock 1302, by setting a register equal to FORCUR equal to a set pointvalue STPNT (set at block 929 in subroutine USER, FIG. 33B) multipliedby K₁. From block 1302, the program proceeds, at block 1304, tocalculate a period error (which is of course, not the same as thevoltage error calculated at block 1108 in subroutine AVC in FIG. 33I) bycalculating the difference between STPNT and PERD, PERD havingpreviously been calculated by subroutine COMPUT as described above.Next, at block 1306, the sign of the period error is calculated; If theerror is positive, a negative error flag is cleared at 1308, whereas ifthe error is negative, the same flag is set at block 1310 and the signof the error is changed since the later parts of the program require apositive error value.

From block 1308 or 1310, the program proceeds, at block 1312, to testwhether the error is greater than a deadband value (set at block 931 insubroutine USER, FIG. 33B). If the error is less than the deadband, nochange in welding current is needed and the program is exited via block1330. If, however, the error is greater than the deadband the error isthen multiplied by a gain control constant K₂ (set at block 933 insubroutine USER, FIG. 33B) at a block 1314 to calculate an error currentI_(E). The program then proceeds, at block 1316, to test whether thenegative error flag previously referred to is set. If not, an increasein welding current is required and I_(E) is added to I_(F) (the previousvalue of the welding current) at block 1318. If, however, at block 1316the negative error flag is set, the welding current must be reduced andthe new welding current value is set equal to the difference betweenI_(F) and I_(E) at block 1320.

From block 1318 or 1320, the program proceeds to block 1322 which is thebeginning of the last section of the program, this last section beingprovided to ensure that the actual current will not be adjusted outsideminimum and maximum limits MINC and MAXC respectively, which arepermanently set in the software but, of course, depend upon theparticular welding apparatus being used. Accordingly, block 1322 testswhether I, the new value of the welding current, is less than MINC, andif so I is set equal to MINC at block 1324. From block 1322 or 1324, theprogram proceeds, block 1326, to test whether I is greater than MAXC; ifso, I is set equal to MAXC at block 1328. From block 1326 and 1328, theprogram is exited via block 1330. Although not shown in FIG. 34, if itis necessary to set the current at either block 1324 or 1328, a warningflag is placed in the system to advise the operator that the programshown in FIG. 34 is attempting the adjust the weld current outside thepreset limits, an indication of possible error in the apparatus.

Using the apparatus and software shown in FIGS. 19-34, a number ofexperimental runs were performed using bead-on-plate welding techniques.Conditions were varied to provide a wide variety of weld pool sizes andoscillation frequencies. The results of these returns are shown in Table1 below:

                  TABLE I                                                         ______________________________________                                                                      Pool                                                 Base     Travel   Arc    Osc.  Pool  Pool                                Run  Current  Speed    Voltage                                                                              Freq. Width Depth                               #    (Amps)   (in/min) (volts)                                                                              (Hz.) (in.) (in.)                               ______________________________________                                        1    100      1        9.4    306   .206  .188                                2    100      1        10.4   273   .191  .169                                3    100      1        11.3   208   .225  .197                                4     75      1        9.2    416   .163  .122                                5     75      1        10.2   348   .150  .131                                6     75      1        11.2   300   .163  .125                                7    100      2        10.2   250   .181  .197                                8    100      2        9.2    375   .144  .181                                9     75      2        10.2   312   .138  .138                                10    75      2        9.1    394   .144  .122                                11    75      2        11.0   312   .144  .141                                12   100      3        9.3    319   .119  .144                                13   100      3        10.0   306   .144  .125                                14    75      3        10.2   326   .122  .122                                15    75      3        9.2    429   .116  .106                                16    75      .5       10.2   333   .206  .156                                17    75      .5       11.0   300   .213  .144                                18   100      .5       11.0   219   .225  .200                                19   100      .5       10.0   273   .231  .169                                20   100      .5       12.3   167   .238  .188                                21   100      2        10.0   273   .138  .163                                22   100      1        10.0   288   .175  .169                                23   100      1        11.0   221   .200  .206                                24   100      1        11.5   183   .238  .200                                25   100      1        12.0   155   .231  .225                                26   100      1        12.5   147   .263  .219                                27   100      1        13.0   133   .275  .231                                28   100      2        11.5   214   .169  .169                                29   100      2        12.1   185   .181  .175                                30   100      2        13.0   161   .225  .219                                31   100      1        13.6   115   .263  .238                                32   100      1        14.0   136   .250  .206                                33   100      2        13.4   140   .200  .188                                ______________________________________                                    

The weld pool width and depth quoted in Table 1 above were determined bythe standard techniques of making a cut through the completed weld, andpolishing and etching the exposed surface to reveal the shape of theweld pool and finally manually measure the width and depth. The data inTable 1 were analyzed by multiple linear regression analysis forvariation of weld pool oscillation frequency with weld pool width anddepth and the best fit was found to be given by the equation:

    F=19.5W.sup.-0.42 B.sup.-1.02                              (1)

where F is the weld pool oscillation frequency in hertz and W and D arethe weld pool width and depth respectively in inches. The coefficient ofcorrelation (R²) for the data in Table using the above equation was0.7368.

A second round of multiple linear regression analysis was performed onthe data in Table 1 because plotting of the data suggested aninterrelationship between arc voltage and weld pool oscillationfrequency. Accordingly, it was felt that including one of the weldingparameters as an extra term in the equation would improve thecorrelation significantly. However, the welding parameter chosen was arclength rather than arc voltage because arc length is more readilycontrollable than arc voltage, being precisely controllable by theZ-axis translator of the apparatus.

This second run of multiple linear regression analysis produced thefinal equation mentioned in the introductory part of this section of theapplication; namely:

    F=19.4W.sup.0.033 B.sup.-0.77 H.sup.-0.35                  (2)

where H is the arc length in inches and F,W and D are as given above.

The coefficient of correlation against equation (2) for the data inTable 1 is 0.912, showing the significant improvement in correlationobtainable by allowing for arc length. Because the variation of F with Wis so small, the algorithm described above with reference to FIG. 29 andimplemented by the program shown in FIG. 34 is capable of producing veryuniform weld pool dimensions by maintaining the oscillation frequency,and hence the mass, of the weld pool constant without direct measurementof weld pool width. Nevertheless, as previously mentioned, the weld pooloscillation frequency measuring apparatus and associated software shownin FIGS. 19-34 are designed so that a single set of welding apparatuscan incorporate both weld pool oscillation frequency measurement and theweld pool width measurement apparatus and software described above withreference to FIGS. 1-18. Such apparatus incorporating both weld pooloscillation frequency and weld width control is capable of real timeanalysis and control of both weld pool oscillation frequency, and hencemass, and weld pool width to provide a very high degree of control ofthe weld process. Also as mentioned above, simultaneous control of weldpool mass and weld pool width will permit control of weld poolpenetration, thereby permitting closely-controlled welds with less thanfull weld penetration.

Although the weld pool oscillation measuring apparatus and softwareshown in FIGS. 19-34 use a very linear power supply to remove allaberrations which might interfere with natural weld pool oscillation, itwill be appreciated that the need for such very linear power supplies,which might not be suitable in a commercial apparatus, can be avoided byusing more sophisticated mathematical techniques. In particular, if thecyclic variation in arc voltage after weld current pulsing is subjectedto Fourier analysis by methods which will be known to those skilled inthe art, aberrations of known frequency in the power supply can beremoved from the arc voltage curve and the natural frequency of the poolthereby analyzed.

It will also be apparent to those skilled in the art that oscillation ofthe weld pool in the instant weld pool oscillation methods may beachieved by methods other than pulsing the welding current, currentpulsing being used in the preferred instant apparatus because of itsability to produce a known level of weld pool disturbance on demand andwith accurate repetition. For example, weld pool oscillation could beinduced by striking the weld joint preparation with a hammer or similarinstrument, or a piezo-electric or other vibrator could be mounted onthe weld joint preparation to drive weld pool oscillations.

REFLECTED BEAM APPARATUS

FIG. 35 shows a schematic side elevation of a first reflected beamapparatus of the invention being used to track the weld line 1554 (FIG.36) in a bevel groove type weld joint preparation comprising twoportions 1520 and 1522 of base metal have their adjacent edges beveledso as to form a groove 1552 (FIG. 36) in the center of which lies theweld line 1554 (FIG. 36).

The reflected beam apparatus shown in FIG. 35 is intended for use in gasmetal arc welding (GMAW) and includes a consumable welding electrode1524 disposed adjacent the weld line of the weld joint preparation. Thereflected beam apparatus and method of the invention are especiallysuitable for use in GMAW using a consumable electrode, since theconsumable electrode will normally have a surface which is cleaner, andhence more reflective, than other types of electrodes. However, thereflected beam apparatus and method of the invention can be practicedwith other types of electrodes, although in some cases polishing orother treatment of the electrode may be necessary to produce asufficiently reflective surface. It should be noted that in FIG. 35 theapparatus is shown in a condition prior to welding with no arcestablished between the electrode 1524 and the weld joint preparation;it is one of the advantages of the reflected beam apparatus and methodof the invention that detection of the weld line can be effected priorto the start of the welding process, and the apparatus and method thusused to position the welding electrode accurately on the weld linebefore welding commences.

The electrode 1524 is surrounded by a cylindrical gas retention tube1530 which serves the conventional function of retaining the purge gasaround the electrode 1524. The tube 1530 is provided with a cylindricalside branch 1542 having an axis which forms an acute angle with the axisof the main part of the tube 1530. A laser beam 1526 generated by alaser 1528 (which is preferably a helium-neon laser) is directed axiallythrough the side branch 1542 so as to strike the electrode 1524 at apoint spaced from, but close to, the tip of the electrode 1524. The beam1526 is thus reflected from the reflective surface of the electrode 1524to form an illuminated area on the weld joint preparation; the nature ofthis illuminated area will be discussed further below with reference toFIG. 36. Light from this illuminated area reflected approximatelyparallel to the axis of the electrode 24 passes up the tube 1530 as abeam 1532 and strikes a mirror 1534 fixedly mounted within the tube 1530at 45° to the axis of the electrode 1524. The mirror 1530 is providedwith a central aperture to allow the electrode 1524 to passtherethrough. After reflection from the mirror 1534, the beam leaves thetube 1530 via an aperture provided in the tube 1530 adjacent the mirror1534 and is collimated by a convex lens 1536 to produce a parallel beamof light which passes through a second convex lens 1538 to form an imagein an image plane 1540. As in the apparatus shown in FIGS. 1-3, theimage in the image plane 1540 may be observed by eye but in practice theimage plane 1540 will normally be occupied by a video camera whichgenerates a video signal representative of the image, and it is thisvideo signal which is normally used for analysis of the image producedby the apparatus shown in FIG. 35. Those skilled in the art willappreciate that the collimating lens 1536 is not absolutely necessarybut is desirable for the same reasons as described above with referenceto the apparatus shown in FIG. 1.

Obviously, in the apparatus shown in FIG. 35 the illuminated area on theweld joint preparation must be sufficiently small that it can be seen bythe optical system just described, which in effect looks down the tube1534. To produce a sufficiently small illuminated area, the apparatusshould be arranged so that the laser beam 1526 strikes the electrode1524 close to, but not coincident with, the tip of the electrode and theangle A between the axis of the laser beam 1526 and the plane normal tothe axis of the electrode 1524 should be made as large as possible. Whenthe apparatus shown in FIG. 35 is actually being used for welding, thetube 1542 serves to prevent smoke rising from the welding operationobscuring the laser beam 1526.

The laser beam 1526 desirably has a width approximately equal to thewidth of the electrode 1524 at the point where the beam strikes theelectrode, the widths of the beam and the electrode both being measuredalong an axis normal to both the axis of the beam and the axis of theelectrode. Normally, of course, both the beam and the electrode will becircular and it is only necessary to make the diameter of the beam equalto the diameter of the electrode. Using a beam having a diameterapproximately equal to the diameter of the electrode produces anapproximately annular illuminated area on the weld joint preparation, aswill be described below with reference to FIG. 36. Using a beam which istoo narrow will produce an illuminated area having the form of only asmall arc of an annulus, which will lead to difficulties if the arc doesnot intersect the weld line, while using a beam which is too wide mayresult in undersirable direct illumination of the weld joint preparationby that part of the laser beam which misses the electrode.

FIG. 36 shows the illuminated area produced on the bevel groove typeweld joint preparation as shown in FIG. 35 when the laser beam 1526shown in that figure has a diameter approximately equal to the diameterof the cylindrical electrode 1524. As will be seen, from FIG. 36, theilluminated area 1546 has substantially the form of a complete annulus.The use of a circular cross-section electrode is preferred so that asimple annular illuminated area is produced on the weld jointpreparation. The form of the illuminated area shown in FIG. 36 is highlyidealized. In practice, the illuminated area is most stronglyilluminated on the side of the electrode facing the incident beam, andthe intensity of illumination decreases in both directions as oneproceeds around the annular illuminated area until, on the side of theelectrode facing away from the incident beam, the intensity ofillumination falls to zero. The electrode of course casts a shadow onthe weld joint preparation on the side of the electrode facing away fromthe incident beam.)

Where the annulus 1546 crosses the beveled edges 1552 of the metalportions 1520 and 1522 and the weld line 1554, an irregularity 1550occurs in the annulus 1546, this irregularity 1550 having the form of aV-shaped deformation with the point of the V extending away from thecenter of the annulus. When the apparatus shown in FIG. 35 has not beenused to weld the metal portions 1520 and 1522 together, there will ofcourse be two such V-deformations in the annulus 1546, whereas duringactual welding there will be only one such deformation since the groovebehind the electrode will be filled with resolidified metal from thealready-completed portion of the weld. The process described below forautomatic tracking of the weld line detects the position of the weldline by analyzing video data along lines such as the line 1551 shown inFIG. 36, this line 1551 extending through the V-shaped deformation 1550.

As already mentioned, the illuminated area 1546 shown in FIG. 36 isproduced using a cylindrical electrode. As will be apparent to thoseskilled in the art, electrodes having other cross-sections will producedifferent illuminated areas, with the adaption of the weld line locationmethods described below to illuminate areas produced from non-circularcross-section electrodes is believed to be within the competence ofthose skilled in the art. Also, of course, the exact type ofirregularity in the illuminated area depends upon the nature of the weldjoint preparation; for example, if the weld joint preparation is of thebutt type rather than the bevel groove type shown in FIGS. 35 and 36,the irregularity where the illuminated area crosses the weld line willhave the form of a dark gap in the illuminated area.

It will also be apparent to those skilled in the art that the reflectedbeam apparatus of the invention does not necessarily have to view theilluminated area axially of the electrode; for example, the illuminatedarea could be viewed by a video camera looking obliquely at theilluminated area. However, as in the other methods of the inventionpreviously described, axial viewing is preferred in order that, duringthe welding operation the very bright arc will be obscured by theelectrode so that no image of the arc appears in the image plane 1540(FIG. 35). Obviously, elimination of the very bright light from the arcmakes it much easier to view the illuminated area and locate theirregularities.

FIG. 37 shows a second reflected beam apparatus of the invention whichallows simultaneous tracking of weld line and analysis of the weld pool.The apparatus shown in FIG. 37 is closely similar to that shown in FIG.1 and is also intended for GTAW. However, the apparatus shown in FIG. 37also incorporates means to reflect a laser beam off the weldingelectrode.

In FIG. 37, an electrode holder 1562 supports an L-shaped electrodehaving two sections at right angles to one another, namely a horizontalsection 1561 adjacent the electrode holder 1562 and a vertical section1561 which extends vertically downwardly from the end of the horizontalsection 1560. FIG. 37 shows the apparatus in use; from the tip 1563 atthe lower end of the vertical section 1561 of the electrode, an electricarc (omitted from FIG. 37 for the sake of clarity) extends to a bevelgroove type weld joint preparation comprising metal portions 1566 and1567. The adjacent edges 1564 of the metal portions 1566 and 1567 arebevelled to form a groove in which resides a molten weld pool 1570formed by the electric arc. The vertical section 1561 of the electrodeis surrounded by a cylindrical gas retention tube 1572, which serves toretain inert purge gas around the electrode. The tube 1572 is providedwith a side branch 1573 which accommodates the horizontal section 1560of the electrode and the electrode holder 1562.

A helium-neon laser 1576 directs its beam 1574 onto a mirror 1578 whichdeflects the beam 1574 through an aperture 1568 provided in the wall ofthe tube 1572 onto the vertical section 1561 of the electrode. As in theapparatus shown in FIG. 35, the laser beam is reflected off theelectrode to form an annular illuminated area on the weld jointpreparation; it should be noted that the position at which the beamstrikes the electrode is arranged so that this illuminated area liesoutside the weld pool 1570. Rays 1580 of light from the weld pool andsurrounding portions of the weld joint preparation travelingsubstantially parallel to but spaced from the axis of the verticalsection 1561 of the electrode travel up the tube 1572 as a beam 1582. Aswill be apparent to those skilled in the art, the beam 1582 includesboth light from the arc reflected from the weld pool and surroundingparts of the weld joint preparation and laser light originating from theaforementioned illuminated area produced by the reflection of the laserlight from the vertical section 1561 of the electrode. The beam 1582 iscollimated by a collimating lens 1584, deflected from a mirror 1586,passed through a filter 1592 and finally passed through a convex lens1588 which forms an image of the weld pool and surrounding area of theweld joint preparation, including the aforementioned illuminated area,on an image plane 1590 which will, as in apparatus of the inventionpreviously described, normally be occupied by a video camera. The filter1592 is arranged to pass a narrow band of wavelengths including thefrequency of the helium-neon laser 76, thereby reducing the intensity ofthe reflected light from the arc relative to the reflected laser lightfrom the illuminated area. As in the apparatus of the inventionpreviously described, the image in the image plane 1590 does not includean image of the arc, since direct light from the arc is blocked by thevertical section 1561 of the electrode.

As will be appreciated by those skilled in the art, a tungsten orsimilar nonconsumable electrode tends to develop a relativelynon-reflectively oxide coating after a period of welding an it may benecessary to remove this oxide coating by polishing or a similartechnique at appropriate intervals in order that the portion of theelectrode upon which the beam impinges will be sufficiently reflectiveto produce a proper illuminated area upon the weld joint preparation.

The manner in which video data from the apparatus shown in FIG. 35 or 37is analyzed automatically to locate the weld line is described below. Itshould be noted that, since the instant reflected beam apparatus can bearranged so that the illuminated area forms just outside the weld pool,it will normally not be necessary to build in delay techniques to allowfor the distance between the point at which the weld line is detectedand the actual position of the welding torch, such as are necessary inprior art techniques in which tracking of the weld line occurs asubstantial distance in front of the welding torch.

REFLECTED BEAM METHOD

The software used to carry out the instant reflected beam method onbevel type weld joint preparations is shown in FIGS. 39-42. FIG. 39shows the overall architecture of the software, with FIGS. 40-42 showingthe subroutines TRACK, LNGRES and CONTROL mentioned in FIG. 39. Unlikethe weld pool width measuring software described above with reference toFIGS. 15 and 17-17H, the software shown in FIGS. 39-42 is not designedto act upon a single row of video data, but rather upon a plurality oflines such as line 1551 in FIG. 36. As will be apparent from thedetailed description of the software below, the software locates theweld point line by finding the intersection of lines such as 1551 withthe V-shaped irregularity 1550, and then applying linear regression tothe two sets of points detected, thereby locating the two linesconstituting the irregularity 1550. Finally, the point of intersectionof these two lines of the irregularity 1550 is calculated, therebylocating the tip of the V-shaped irregularity, which lies on the weldline.

The selection of an appropriate window for use in this method is thus amatter for the skill and judgement of the operator, but obviously it isdesirable to restrict the width of the window, (i.e. restrict the numberof columns from which video data are accepted) since the width of theimage of the irregularity is much less than the full width of thescreen. In order to locate the intersections of the scan lines such asline 1551 with the irregularity, it is desirable that, if possible, therow skip value be set to zero so that no pixels are skipped within eachaccepted line. However, since the aim of the software is to locate theintersections of lines such as 1551 with the two lines constituting theV-shaped irregularity 1550, row skipping is permissible. Indeed, sincethe error in locating the intersections of line 1551 and irregularity1550 will normally be substantially constant regardless of which line ischosen as line 1551, it will be apparent to those familiar with linearregression techniques that, if the number of lines which can be acceptedis limited, it is better to employ row skipping so as to spread theavailable lines over as large as possible an extent of the dimension ofirregularity 1550 parallel to weld line 1552 in order to provide themost accurate location of the lines constituting irregularity 1550. Inmost situations, the image of irregularity 1550 is so small relative tothe whole image seen by the video camera that neither row skipping norcolumn skipping is necessary, especially if the width of the videowindow is restricted.

The upper part of FIG. 38 shows an enlarged view of the area of FIG. 36including the irregularity 1550 and line 1551. Also indicated in theupper part of FIG. 38 are the X and Y axes used in the calculation, theX-axis being taken parallel to the weld line (which in FIG. 38 is alinear weld line) and the Y-axis taken horizontally in FIG. 38.

The graph A in FIG. 38 shows the light intensity on line 1551. It willbe seen that this light intensity comprises a realtively low backgroundlevel on which are superimposed two substantially triangular peaks, thesummit of each peak lying at one of the intersections of the line 1551with irregularity 1550. Graph B in FIG. 38 shows the first derivative ofthe light intensity curve shown in graph A; as those skilled in the artare aware, differentiation of peaks such as those shown in graph Aproduces a first derivative in which the sign of the derivative changesvery abruptly as the curve passes through a peak. Graph C in FIG. 38shows the second derivative of the curve shown in graph A. For presentpurposes, it is only necessary to note that the positions of the peaksin graph A, and thus of the intersections of line 1551 with irregularity1550, are represented by two intense minima in the second derivativecurve shown in graph C. The software shown in FIGS. 39-42 is designed tolocate these two minima in the second derivative curve. However, becausethe graphs shown in FIG. 38 are somewhat idealized, in practice the twomost intense minima in the second derivative of the light intensity maynot represent the true positions of the intersections, theseintersections being represented by other, less intense minima.Accordingly, the software shown in FIGS. 39-42 incorporates checks toscreen out obviously impossible intersection positions.

As already mentioned, FIG. 39 shows the overall architecture of thesoftware used in the weld tracking method for bevel type weld jointpreparations. From a starting point at block 1700, the program proceedsto a memory assignment and initialization block 1702, which assignsareas in memory for the various data which will be generated during theprogram and initializes various registers. Since this type of memoryassignment and initialization routine will be familiar to those skilledin the art, it is not necessary to describe it further. Next, at block1704, an initialization and "get parameters" routine is performed, inwhich the software acquires the necessary parameters, including thefirst and last row end column values and the row skip and column skipvalues which are used to define the windows without which thevideo-computer interface is to store data. (Although it is not explicitymentioned in the description of FIG. 15 above, it will be apparent tothose skilled in the art that block 402 in FIG. 15 includes a subroutinesimilar to the subroutine USER (FIG. 33B) to enable the operator toenter the parameters required by the video-computer interface. Since theparameter entered at block 402 include all the parameters required bythe software shown in FIGS. 39-42, the latter software simply acquiresthe parameters its needs at block 1704 and thus requires no separatesubroutine for handling keyboard inputs. Thereafter, at block 1706, theprogram sets the COM/CAM signal low, thereby instructing thevideo-computer interface to acquire video data from the camera. Theprogram then waits, at block 1708, for the negative transition of theEOF signal, which indicates acquisition of video data from the completewindow by the video-computer interface. (As previously mentioned, thenegative transition of the EOF signal does not exactly correspond withthe end of the acquisition of video data and therefore, of course, block1708 incorporates a further small delay to ensure that all video datafrom the window have been acquired by the video-computer interfacebefore the later processing steps of the program are executed.) Once theprogram has waited at block 1708 for the appropriate period, it proceedsto block 1710, where the COM/CAM signal is set high, thereby preventingthe video-computer interface from acquiring further data and allowingthe computer to read the previously-acquired video data from theinterface. The program then proceeds through subroutines TRACK, LNGRESand CONTROL at blocks 1712, 1714 and 1716 respectively to analyze thevideo data received from the interface and thus to locate the weld lineand generate control signals which can be supplied to an apparatus suchas that shown in FIG. 18 or 19 and thus to control the movement ofwelding electrode. From block 1716, the program loops back to block 1706for a further round of video data acquisition and analysis.

Subroutine TRACK is shown in more detail in FIG. 40. This subroutinedetects the intersections of the camera scan lines, such as line 1551 inFIGS. 36 and 38, by generating the second derivative of the lightintensity data curve and by finding the minima therein. The subroutinealso provides checks to reject spurious minima.

As shown in FIG. 40, subroutine TRACK commences, at block 1720, bysetting a counter I=to 0. Counter I is a counter which counts rowswithin the window of accepted video data, while counter J mentionedbelow counts pixels within the accepted part of each accepted row of thewindow. The maximum allowable values of I and J, designated I_(max) andJ_(max) below, are of course dependent upon the first and last row andcolumn values and the row skip and column skip values entered by theoperator at block 1704 (FIG. 39) and are in fact calculated by theprogram at block 1704. Next, at block 1722, I is incremented by 1, thenat block 1724 J is set equal to zero and at block 1726 incremented by 1.The program then proceeds at block 1728, to read DATA (I,J) from thevideo computer interface into an appropriate table of the computermemory. (It will be noted from the foregoing description of the videocomputer interface that video data from accepted pixels are simplystored in successive locations within the memory of the video-computerinterface beginning with address 0. Accordingly, block 1728 mustincorporate means to calculate the address within the memory at whichDATA (I,J) is located. Calculation of the necessary address is of courseeasily accomplished by methods which will be familiar to those skilledin the art.) It should be noted that the table designated DATA(I,J) atblock 1728 in FIG. 40 is the table of raw video data stored in thememory of the computer and is not equivalent to the table DATAcontaining smoothed video data described above with reference to FIGS.17-17H. In the program shown in FIGS. 39-42, smoothing of the videoprior to analysis is not desirable since this would tend to flatten outthe peaks in the video data and make the location of the minima in thesecond derivative curve representing the intersection of the camera scanlines with the irregularity 1550 (FIG. 36) less precise.

Following block 1728, the program tests, at block 1729, whether J isequal to its maximum allowable value, J_(max). If not, the program loopsback to block 1726. Accordingly, it will be seen that the effect ofblocks 1726, 1728 and 1729 is to transfer all the video data for the Ithaccepted line from the video-computer interface to the computer memory.Once this has been achieved, when J is equal to J_(max), block 1729produces a positive result and the program proceeds, at block 1730, torun a subroutine DERIVSEC, which determines the second derivative of theset of data for the Ith accepted line now stored in the computer memory.Those skilled in the art will be familiar with various subroutines whichmay be used as the subroutine DERIVSEC; for example, such a subroutineneed only comprise two successive passes through a differencing blocksuch as block 502 in FIG. 17C. Accordingly, it is believed that nofurther description of the subroutine DERIVSEC is required. Next, atblock 1732, the program performs an inverse bubble sort on the secondderivative values generated at block 1730 i.e. block 1732 arranges thesecond derivative values in increasing order so that the first values inthe rearranged table represent minima in the second derivative curve,the strongest minima being located in the first few positions in therearranged table. It should be noted that, since it is the positions ofthe minima in the second derivative curve which are required rather thanthe actual minimum values, what block 1732 actually does is to performan inverse bubble sort on the second derivative values, andsimultaneously compile a corresponding table, designated M(K), whichshows the corresponding locations from which the rearranged secondderivative data were produced i.e. M(K) is a table of locations arrangedin increasing order of the corresponding second derivative data.

The program then proceeds, at block 1734 to set a counter i=1 and then,at block 1736, to set X(I,i) equal to M(i), and then to increment i. iIs then tested at block 1737 to see if it is equal to 2; if not, theprogram loops back to block 1734. It will be seen that the programproceeds through blocks 1734, 1736 and 1737 twice, thereby writing M(1)and M(2) into X(I,1) and X(I,2) respectively. Thus, X becomes a tableeach line of which represents the locations of the two most intenseminima found in the second derivative of the video data from the Ithaccepted line.

After the second pass through block 1736, block 1737 produces a positiveresult and the program proceeds to block 1739 where it tests whether Iis equal to 1 i.e. whether the data being handled relate to the firstaccepted line of the window. If so, there are no previous values intable X with which the locations just placed in X(1,1) and X(1,2) can becompared and accordingly the program loops back from block 1739 to block1722 and proceeds to deal with data from the second line in the manneralready described. If, however, I is greater than 1, the programproceeds from block 1739 to block 1738, which is the first of a sequenceof operations designed to check that the locations of the secondderivative minima placed in X by block 1736 are true locations ofintersections by comparing these locations with locations from theprevious line of data.

Block 1738 compares X(I,1) with X(I-1,1) and X(I-1,2) i.e. with theminima locations found on the previous line. If X(I,1) is in fact a trueminimum location, it will lie within a distance Z (an operator-fixedparameter representing an allowable range of variation in locationposition between adjacent lines) of one of the minima locations for theprevious line; note that since there has been no previous attempt tosort X(I,1) and (XI,2) by magnitude, the relative magnitudes of thesetwo locations are not fixed and X(I,1) may correspond to either of theminima locations found in the previous line, so that the alternativetests shown in block 1738 is necessary. If block 1738 produces anegative result, X(I,1) is a false minimum and it is hence discarded atblock 1740, X(I,2) being written into X(I,1) and M(3) being written intoX(I,2). Note that block 1740 actually replaces X(I,2) with M(i+1) sothat, should block 1738 detect at least two false minima locations insuccession, necessitating two, or perhaps even more, passes throughblock 1740, different minima will be placed in X(I,1) and X(I,2) on eachpass through block 1740. From block 1740, the program loops back toblock 1738. Thus, block 1738 will only produce a true result when it isdetermined that X(I,1) represent a true minimum. When this occurs, theprogram proceeds to block 1742. Blocks 1742 and 1744 are exactlyparallel to blocks 1738 and 1740 respectively, except that they testwhether X(I,2) is a true minimum location, and that at block 1744 it isof course not necessary to change X(I,1) since this has already beendetermined to be a true minimum location at block 1738.

When block 1742 produces a positive result, the program proceeds, atblock 1746, to test the relative magnitude of the two true minimalocations now present in X(I,1) and X(I,2). As previously noted, therehas been no previous attempt to determine the relative magnitudes ofthese two locations, so either can represent either the left-hand orright-hand intersection in FIG. 38. Obviously, for the linear regressionanalysis to be carried out by subroutine LNGRES (see below) to operateproperly, it is essential to arrange X so that the values of X(I,1)represent the intersections where the left-hand line in FIG. 38 and thevalues in X(I,2) represent intersections with the right-hand line inFIG. 38. Accordingly, if block 1746 produces a negative result, the twominima locations in X(I,1) and X(I,2) are interchanged from block 1748.From block 1748, or if block 1748 produces a positive result, theprogram proceeds, at block 1749, to test whether I_(max) i.e. whetherall accepted lines have been processed. If not, the program loops backto block 1722 and proceeds to deal with the next line, but if block 1749produces a positive result, subroutine TRACK is exited via a block 1750and proceeds to subroutine to LNGRES shown in FIG. 41.

As shown in FIG. 41, subroutine LNGRES first, at block 1760, performslinear regression on the minima locations in X(I,1) to derive aregression equation for the left-hand line of irregularity 1550 (FIG.38). The program then proceeds to block 1762 and performs a similarlinear regression operation on the date in X(I,2) to derive the equationacross the right-hand line of irregularity 1550. Since the appropriatelinear regression equation and modes of implementing them on computerswill be apparent to those skilled in the art, no further description ofblocks 1760 and 1762 is required. The program then proceeds, at block1764, to solve the two equations thus generated to determine X and Y,the coordinates of the tip of the V-shaped irregularity 1550, this tiprepresenting, as previously mentioned, the point on the weld line.

In a typical commercial bevel type weld joint preparation, the slopingsurfaces 1520 (FIG. 35) lie at an angle of approximately 45° to thehorizontal surfaces of the metal portions, the angle between the twolines of irregularity 1550 (FIG. 36) is approximately 90°, so thatslight errors in the equations of the two lines constitutingirregularity 1550 do not produce inordinate errors in location of thepoint of intersection.

Following block 1764, subroutine LNGRES is exited at block 1766 and theprogram proceeds to subroutine CONTROL shown in FIG. 42. As shown inthat FIG. subroutine CONTROL first procures, at block 1770, X and Yset-points SPX and SPY respectively, which were obtained at block 1704(FIG. 39), and which represent the desired location of the point on theweld line represented by the tip of irregularity 1550 (FIG. 38). Next,at block 1774, the program calculates a horizontal correction signal HORequal to a constant, k₁, times the difference between the actual valueof Y determined by subroutine LNGRES and SPY, the desired value of Y.Thereafter, its associated circuit at block 1776, a vertical directionsignal VER is calculated as a constant k₂, times the difference betweenthe actual and desired values of X. Subroutine CONTROL is then exitedvia block 1778.

The horizontal and vertical correction signals generated by subroutineCONTROL can be applied to Y-axis and Z-axis translators respectively inorder to bring the position of the detected point on the weld line backto its desired position; note that a vertical correction is requiredsince the radius of the circle 1546 (FIG. 36) and thus the position ofthe tip of the irregularity 1550 which is the point (X,Y) is dependentupon the vertical position of the welding electrode. No correction tothe X-axis translator is required since this translator is moving thewelding electrode at the desired welding speed along the X-axis. Thus,the third weld tracking method described above not only serves to locatethe weld line, but can also be used to maintain the welding electrode aproper distance from the weld join preparation.

It will be apparent to those skilled in the art that the control modeeffected by subroutine CONTROL is a relatively simple one which might,depending upon the values chosen for k₁ and k₂, tend to produce hunting.If desired, subroutine CONTROL could be modified to average thehorizontal and vertical corrections signals over a period of time,thereby dampening the movement of the X-axis and Z-axis translators toprevent hunting.

It will also be apparent to those skilled in the art that the softwareshown in FIGS. 39-42 represents a very simple method of following theweld line and that considerably more sophisticated techniques may bedesirable to cope with various problems which may be encountered inpractice. In particular, the checks carried out by subroutine TRACKshown in FIG. 40 depend upon finding two proper minima in the first linein which such minima are present and thereafter comparing minima in eachsubsequent line with the position of the minima in the immediatelypreceding line. Obviously, if one or both of the minima found in thefirst line are false, there is no guarantee that proper minima will belocated and thus the linear regression analysis will not give properresults. Also, the software shown in FIGS. 39-42 is only intended tocope with relatively minor deviations in the direction of the weld line;essentially, this software is intended for use with weld lines which areintended to be linear but which in practice deviate by a few degreeseither way from the intended direction. As already mentioned, in atypical bevel type weld joint preparation the two lines constituting theirregularity 1550 meet at approximately 90°. Accordingly, if the weldline 1554 deviates by more than about 45° from the intended vertical (inFIG. 38) direction, none of the scan lines of the camera, such as theline 1551 in FIGS. 36 and 38, will yield two true intersections with theirregularity 1550 and the software will become inoperable.

Those skilled in the art will be aware of various techniques which couldbe used to overcome these problems. Firstly, subroutine TRACK shown inFIG. 40 could be modified to check that all the minima are tested fordepth before being placed in matrix X in order to ensure that onlyminima which has sufficient depth to give a reasonable assurance thatthey are true minima are placed in matrix X. Secondly, a relativelystraightforward modification of blocks 1738-1744 in FIG. 40 can be madeso that if a line generates only one acceptable minimum, the minimapresent in the next line are compared with only the one acceptableminimum present in the preceding line, thereby allowing one series ofpoints defining one of the two lines constituting the irregularity 1550to be begun before the other. (As will be apparent from consideration ofFIG. 38, it will only take a relatively small deviation of the weld line1554 from the ideal position for a few scan lines to yield a trueintersection with one side of the irregularity but not with the other.)When a later scan line yields two acceptable minima, the second set ofdata, representing the other side of the irregularity 1550, can bebegun.

Guarding against aberrant minima in the first scan line to detect suchminima is more difficult. One might compare the apparent intersectionson the first line where the corresponding values for the first line onthe preceding analysis or (probably better) compare the actualintersection positions found for the first line with those calculatedfrom the linear regression lines generated during the previous frameanalyzed. Alternatively, one might locate provisional intersectionpositions for the first few lines generating acceptable minima, groupthese apparent intersection positions into two groups representing theapparent sides of the irregularity 1550 and then average the resultingvalues. Even if one of the provisional minima represents an aberrantminimum, the average should give a reasonably accurate value for a truelocation, which can then be used to check the provisional values andeliminate false ones.

If the apparatus and software shown in FIGS. 35-42 is used to track weldlines which undergo considerable changes in direction, it will benecessary to ensure that the position of the weld line as seen by thecamera does not deviate by more than about 30° from the ideal positionshown in FIG. 38, in order to ensure that there will be at least a fewscan lines which do generate two genuine intersections with theirregularity 1550. One simple way to cope with very curved weld lines isto mount the camera so that it is rotatable about the axis of thewelding electrode and to arrange the software that when the angle ofdeviation of the weld line from the ideal position shown in FIG. 38exceeds about (say) 30°, an "angle error" signal is generated which willcause the camera to rotate about the axis of the welding electrode tostore the position of the weld line, as seen from the camera, to itsoptimum position.

Alternatively, to avoid physical movement of the camera while stillcoping with large movements in the position of the irregularity seen bythe camera, more sophisticated image analysis techniques could beemployed. Firstly, to cope with translations of the irregularity alongthe X and Y axes, one could arrange the software so that once theposition of the tip of the irregularity has been detected in the firstframe, the position of this tip is used to generate signals which alterthe parameters defining the window from which video data is retained bythe video computer interface so that the irregularity remainsappropriately located within this window. Large rotations of theirregularity relative to the camera scan lines can be allowed for bychanging the lines along which the software looks for the intersectionswith the two lines constituting the irregularity 1550. Although thesoftware described above uses the camera scan lines parallel to theY-axis as the line 1551, other lines can obviously be used. Since thelight intensities for each separate accepted pixel are storedindependently in DATA(I,J), lines running at approximately 45° to the Xand Y axes can be constructed by changing both I and J by + or -1simultaneously, and analysis of light intensity along such diagonallines carried out in a manner very similar to that described above withreference to FIG. 40, merely by modification of blocks 1722-1728.Obviously, it is also a simple matter to carry out detection ofintersections by proceeding along lines parallel to the X-axis merely bychanging the order in which I and J are incremented in subroutine TRACK.Accordingly, if subroutine TRACK is modified so that it can carry outthe search for intersections between the analysis lines and theirregularity using any one of four different sets of analysis lines (twoof these sets being parallel to the X and Y-axes respectively, and theother two being diagonal sets at 45° to both axes), it will always bepossible to find a set of lines such that the weld line 1554 (FIG. 38)is within about 221/2° of the perpendicular to one of the sets of lines,which will result in several of the lines in this set generating twogenuine intersections with the irregularity 1551. Also, the softwarewould of course need to be modified so that when the angle between theoptimum position of the weld line for the set of lines being used foranalysis and the actual position of the weld line exceeded (say) about25°, the software would automatically switch to an alternative set ofanalysis lines. It is believed that the necessary modification to thesoftware will readily be apparent to those skilled in the art.

If the software is modified to cope with very large deviations of theweld line from the optimum position, it will also be necessary to modifysubroutines CONTROL shown in FIG. 42. In particular, to allow for verylarge deviations in the direction of the weld line, which will cause theY-axis coordinate of the tip of the irregularity to be comparable tothat of the X-axis coordinate thereof, it will be necessary to generatea X-axis correction signal in order to slow the rate of movement of thewelding electrode along the X-axis in order to prevent the rate ofmovement of the electrode relative to the weld joint preparationbecoming too large. Also, block 1776 in FIG. 42 should be modified sothat the vertical error signal is proportional to [(X² +Y²)^(1/2) -(SPX²+SPY²)^(1/2). Finally, if as suggested above, the software is modifiedso that the window from which video data is retained by the videocomputer interface is modified as the irregularity moves within thefield of view of the camera, it may be necessary to allow for similarautomatic adjustment of SPX and SPY depending upon the position of thewindow at any given time.

It will also be apparent to those skilled in the art that a number ofother control schemes could be utilized to detect a V-shapedirregularity, but all such schemes would appear to necessitate a logicalscheme which is generally similar to that described above with referenceto FIGS. 39-42. Obviously, very different software would be necessaryfor tracking weld lines in butt or other types of weld jointpreparation, but it is believed that development of such software iswithin the skill of those skilled in the art. In the case of butt typeweld joint preparation, in which the weld line will appear as a narrowdark strip which will cause a break in the circle 1546 (FIG. 36), atleast two different approaches appear possible. Firstly, one coulddetect the intersections of the camera scan lines with the circle 1546by looking for minima in the second derivative of the light intensitycurve by the technique described above for finding intersections of line1551 with irregularity 1550. One could then search for a dark striplocated between these intersections by looking for the maximum andminimum in the first derivative of the light intensity curve whichshould be associated with the edges of the strip. Finding the mid-pointbetween the first derivative maximum and minimum should locate the weldline with sufficient accuracy. An alternative and better method would beto detect the intersections of the camera scan lines with the circle1546 (FIG. 36) as already described, to fit the resultant points ofintersection to the equation of a circle and then to track around thiscircle, using curve-following techniques which will be familiar to thoseskilled in the art, to locate the point at which the intensity of thecircle diminishes very suddenly, thus detecting the gap in the circlecaused by the weld line.

LOW POWER ARC APPARATUS AND METHOD

FIG. 43 shows a low power arc apparatus of the invention being used tolocate a welding electrode in its proper position relative to a weldline prior to beginning welding. FIG. 43 shows a welding electrode 1600,which is surrounded by a cylindrical gas retention tube 1608. Theelectrode 1600 is disposed adjacent a weld joint preparation of thebevel groove type, this weld joint preparation comprising two metalportions 1602 and 1603 disposed adjacent one another, their adjacentedges being beveled so as to define a groove 1604 at the center of whichlies the weld line. A very low current arc 1606 has been establishedbetween the electrode 1600 and the weld joint preparation; this arc isof sufficiently low power that no weld pool is formed on the weld jointpreparation but is of sufficient power to generate light. Light from thearc is reflected from the weld joint preparation, both from the flatsurfaces of the metal portions spaced from the groove, and from thebeveled edges of the groove 1604. Rays of light traveling substantiallyparallel to, but spaced from, the axis of the electrode 1600, includingrays such as 1609 reflected from the flat surface of the metal portion1603 and rays such as 1610 reflected from the beveled sides of thegroove 1604, pass up the tube 1608 and are thereafter brought togetherto form an image by an appropriate axial viewing system of theinvention, such as those shown in FIGS. 1-3, 35 or 37. The resultantimage shows the area of the weld joint preparation surrounding theelectrode 1600 and, as usual, does not include a view of the arc 1606,since the axial viewing position causes the arc to be obscured by thetip of the electrode. Because of the reflection of light from the wallsof the groove 1604, the groove will show up as an irregularity on theimage and will thus be located. Obviously, it is necessary that thewelding electrode be placed close enough to the groove 1604 that thegroove can be seen in the image obtained by looking down the tube 1608.

It will be appreciated that, of course, if the weld joint preparation isof the butt type rather that the bevel groove type, the weld line willappear in the image seen by means of the axial viewing system as a darkline or strip rather than by reflection of light from the walls of agroove.

To carry out the low power arc method of the invention, an operatorinitially locates the electrode at a point near the weld line, lowersthe electrode in contact with at least one of the metal portions of theweld joint preparation, initiates current flow at a predetermined, verylow level and withdraws the electrode slowly to establish a low currentarc insufficient to melt the metal of the weld joint preparation. Theoperator may continue to withdraw the electrode until such time as thearc is broken. While the low power arc exists, image of the area of theweld joint preparation surrounding the electrode is formed in the manneralready described and the weld line located either visually by anoperator viewing a video monitor or by automatic analysis of the imageby a computer. The electrode is then properly aligned with the weld lineand normal welding can commence.

Obviously, a portion of the image seen using the apparatus shown in FIG.43 may be retained in the memory of a video computer interface such asthat described above with reference to FIGS. 5-13B or described belowwith reference to FIGS. 45-51 and the stored portion of the imagethereafter analyzed to determine the weld line. Also, the image may ifdesired be recorded on video tape for later analysis. Either of thesestorage techniques may be especially useful if the duration of the lowpower arc is very short e.g. if the operator is unable to determine theposition of the weld line visually during the brief interval when a lowpower arc is operating, he could use a video tape recorder with a"freeze-frame" technique to determine the correct position after the arcis extinguished.

FLOWING POOL APPARATUS AND METHOD

FIG. 44A represents a top plan view of a welding operation in which aweld line is being tracked by the instant flowing pool method. A weldjoint preparation of the bevel groove type is formed by two metalportions 1500 and 1501 disposed adjacent one another. The adjacent edgesof the two metal portions 1500 and 1501 are beveled to form bevel faces1503, between which lies the weld line 1502. An arc (omitted from FIG.44A for the sake of clarity) has been struck between a welding electrode1512 and the weld joint preparation, thereby creating a molten weld pool1504 in the groove between the two metal portions. Welding is beingperformed from right to left in FIG. 44A, so that behind the weld pool1504 is an area of resolidified metal 1508 where welding has beencompleted, while a leading portion 1506 of the weld pool is free to flowinto the groove between the two metal portions where welding has yet tobe effected. The relative heights of the areas 1508, 1504 and 1506 maybe better seen from the section in FIG. 44B.

As the leading portion 1506 of the weld pool 1504 flows into the groove,a concave deformation appears in the normally convex surface of the weldpool. When the weld pool is viewed axially of the electrode by an axialviewing apparatus of the invention such as those shown in FIGS. 1-3, 35and 37, this concave deformation in the leading portion 1506 of the weldpool 1504 produces a local minimum of light intensity which can be seenby a human observer but which is perhaps more easily detectedautomatically. In particular, if an image of the weld pool andsurrounding areas shown in FIGS. 44 and 44B is formed by a video camerain which one of the scan lines is a line such as 1510 in FIG. 44Apassing through the leading portion 1506 of the weld pool 1504, thelight intensity along the line 1510 will display three local minima, theusual two local minima associated with the edges of the weld pool (cf.FIG. 16B above) and a central local minimum associated with the concavedeformation and indicating the position of the weld line. Accordingly,the light intensity along the line 1510 may be analyzed to determine thecentral local minimum and hence locate the weld line. Location of thiscentral local minimum is readily effected using the AIM-65 computer inconjunction with a video-computer interface such as those described withreference to FIGS. 5-13B above or 45-51 below, and a modification of thesoftware described above with reference to FIGS. 15 and 17, thismodification generating the positions of three local minima rather thantwo. It is believed that the necessary changes in software will beobvious to those skilled in the art.

Although primarily intended for use in conjunction with bevel type weldjoint preparations, the flowing pool method of the invention may also beused in conjunction with butt type weld joint preparation. In butt-typepreparations, the same type of concave deformation of the welded poolappears, although in this case it is due to the leading portion of theweld pool flowing into the gap between the two metal portions, ratherthan into a groove.

SECOND VIDEO COMPUTER INTERFACE

FIGS. 45-51 show circuit diagrams of the presently preferredvideo-computer interface which can be substituted for that shown inFIGS. 5-13 above. This video-computer interface uses faster memoriesthan that previously described and thus avoids the necessity for theodd/even switching operation in the previous video-computer interface.Also, the video-computer interface shown in FIGS. 45-51 has beenarranged so that all the components can be mounted on a single,specially-prepared printed circuit board which communicates via a singleedge connector with the J1 socket on the standard Rockwell AIM-65 motherboard (for details of this mother board see the manufacturer's manual).This connector provides a 16-line address bus and an 8-line data bus,together with accompanying read/write signal R/W and a clock signal φ2,(which are all shown on the left-hand side of FIG. 45). The letters andnumbers on the extreme left-hand edge of FIG. 45 indicate the lines fromthe computer which carry the relevant signals, in accordance with thestandard nomenclature used in the manufacturer's manual.

As in the video-computer interface previously described, the interfaceshown in FIGS. 45-51 makes extensive use of large scale integratedcircuits, some of which contain several separate circuits. In manycases, the individual circuits on a single chip are used in widelyseparated parts of the circuitry. Hereinafter for convenience, eachintegrated circuit will be given a number prefixed by U and the separatecircuits on the same chip will be indicated by letters following thechip number. Thus, for example, U1A and U1B represent separate circuitslocated on the same chip but used in two different parts of thecircuitry.

The first part of the circuitry shown in FIG. 45 to be described in theblock select circuit indicated by broken boundary 2502 in FIG. 45. Aswill be explained in more detail below, the video-computer interfaceshown in FIGS. 45-51 contains 4K of memory, and this memory must becapable of being addressed by the process control computer. The blockselect circuit 2502 selects which 4K block of memory addresses from thecomputer will be given to the 4K memory in the interface. Since each 4Kblock of memory within the computer is defined by the most significantdigit of a four-digit hexadecimal number, only addresses arriving on thecomputer address bus and having the correct most significant hexadecimaldigit should cause operation of the video-computer interface.Accordingly, the block select circuit 2502 is arranged to generate anenable signal when the most significant hexadecimal digit arriving onthe address bus has a preselected value. For convenience, the blockselect circuit 2502 is arranged so that the most significant digit whichwill cause generation of the enable signal can be varied.

As shown in FIG. 45, line A15 of the address bus, which carries the mostsignificant bit, is fed to pin 5 of an inverter U1A. Integrated circuitU1 comprises a commercially-available 74LS04 integrated circuit, withconventional power connections at pins 14 and 7. The inverted outputfrom pin 6 of U1A is fed to pin 4 of U2, this pin 4 also being connectedto ground via a resistor R200. Integrated circuit U2 is acommercially-available 74LS138 Schottky 1-of-8 decoder/demultiplexerintegrated circuit, provided with the normal power connections at pins16 and 8 as shown in FIG. 45. A +5 V supply line is connected via aresistor R201 to pin 6 of U2, and the same supply line is also passedvia a resistor R202 to pin 11 of an inverter U3A. Integrated circuit U3Ais another commercially-available 74LS04 integrated circuit. Theinverted output from pin 10 of U3A is passed to pin 5 of U2. Since pins4, 5 and 6 of U2 are the enable pins, it will be seen from the truthtable for the 74LS138 that the effect of the inputs to these three pinsis that decoding will only take place when the most significant bitarriving on line A15 is a 1. Thus, the preselected leading hexadecimaldigit can only range from 8 to F.

Lines A12-A14 of the computer address bus are connected to pins 1-3respectively of U2 while the eight outputs from pins 7 and 9-15 of U2are fed to lines 9-16 respectively of a switching assembly S101, whichcomprises eight parallel single pole single throw DIP switches. Theopposite terminals of the switches at pins 8-1 respectively of assemblyS101 are jumpered and the jumpered output (which is a device selectsignal, hereinafter designated DS) passed to two lines 2504 and 2506.

As will be apparent to those skilled in the art, switching assembly S101is set so that one of the switches is closed and the remaining seven areopen. Thus, the jumpered output will be high except when the inputconnected to the closed switch goes low, which will occur only whenlines A12-A15 of the address bus are carrying a predeterminedhexadecimal digit from 8-F. Assembly S101 is illustrated in FIG. 45 withthe switch connecting pins 15 and 2 closed, which sets the predeterminedhexadecimal digit to 9.

The next part of FIG. 45 to be described is the device select circuitindicated by the broken boundary 2508 in FIG. 45. The device selectcircuit serves to provide various enabling signals for controlling theoperation of other parts of the video computer interface. As alreadyexplained, the interface contains 4K (4096) addresses, any one of whichcan be selected by the appropriate signals on lines A0-A11 of theaddress bus. Sixty-four of these addresses do not address memorydirectly; instead, these 64 addresses (combinations of signals on linesA0-A11) are used to control the operation of the interface. The deviceselect circuit also generates a memory inhibit signal which inhibitswriting of data into the memories when the address designated on linesA0-A11 of the address bus is one which does not require writing intomemory.

Lines A4-A11 of the address bus are connected to lines 2, 4, 6, 8, 11,13, 15 and 17 respectively of U4, which is a commercially-available74LS244 inverting Schottky octal buffer/line driver. U4 is provided withthe conventional power connections at pins 20 and 10, while the 1G and2G pins 1 and 19 respectively are connected to a common ground. Theoutput from pin 3 of U4 (corresponding to the signal on line A11) is fedto pin 6 of U5, which is another commercially-available 74LS138 Schottky1-of-8 decoder/demultiplexer. The outputs from pins 12, 9, 7 and 5 of U4(corresponding to the signals on lines A7-A10 respectively of theaddress bus) are fed to pins 9, 10, 12 and 13 respectively of U6A.Integrated circuit U6 is a commercially-available 74LS20 dual 4-inputNAND gate provided with the conventional power connections at pins 14and 7. The output from pin 8 of U6A is fed to pin 5 of U5. The outputsfrom pins 18, 16 and 14 of U4 (corresponding to the signals on linesA4-A6 of the address bus respectively) are fed to pins 1, 2 and 3respectively of U5. The DS signal on line 2506 is fed to pin 4 of U5,thereby ensuring that U5 will only affect decoding when the block selectcircuit 2502 produces a signal indicating that the most significanthexadecimal digit arriving on the address bus has the correctpreselected value. U5 receives the conventional power connections atpins 16 and 8. The output from pin 7 of U5, hereinafter designated CSA,is fed directly to a line 2510, and is also fed to pin 9 of U7A.Integrated circuit U7 is a commercially-available 74LS08 quadruple2-input NAND gate. The output from pin 9 of U5 is fed to pin 10 of U7A.The output at pin 8 of U7A, which is a memory enable (inverse memoryinhibit) signal hereinafter designated MI, is fed to a line 2512.

It will be apparent to those skilled in the art that the effect of theconnections among U5, U6A and U7A is that the enable function E of U5 isgiven by:

    E=A.sub.11.A.sub.10.A.sub.9.A.sub.8.A.sub.7

where A_(x) is the value of the signal on line Ax of the address bus.The value of the signal MI (the inverse of MI) is given by:

    MI=E.A.sub.6.A.sub.5,

while the value of the signal CSA on line 2510 is given by:

    CSA=E.A.sub.6.A.sub.5.A.sub.4

Thus, MI is positive only for the uppermost 32 addresses and CSA ispositive only for the uppermost 16 addresses.

Lines A0-A3 of the address bus (corresponding to the least significanthexadecimal digit) are fed to pins 8, 6, 4 and 2 respectively of U8A.Integrated circuit U8 is another commercially-available 74LS244inverting Schottky octal buffer/line driver provided with the normalpower inputs at pins 20 and 10 and having pins 1 and 19 connected to acommon ground. The output at pin 18 of U8A (corresponding to the signalon line A3 of the address bus) is fed to pin 5 of U9, which is anothercommercially-available 74LS138 Schottky 1-of-8 decoder/demuultiplexer.The outputs at pins 12, 14 and 16 of U8A (corresponding to the signalson lines A0, A1 and A2 respectively of the address bus) are fed to pins1, 2 and 3 respectively of U9. Pin 4 of U9 receives the output from pin9 of U5, while pin 6 of U9 is connected to a line 2514 which, asexplained below, carries a clock signal φ2 from the computer. U9receives the conventional power connections at pins 16 and 8.

It will be apparent to those skilled in the art that U9 will only beenabled for decoding when U5 is enabled, the signals on lines A4-A6 aresuch that the output at pin 9 of U5 goes low, the signal on line A3 ishigh and the signal φ2 on line 2514 is also high. Under theseconditions, U9 will effect decoding of the signals on lines A0, A1 andA2 of the address bus (as inverted by buffer U8A) and one of the outputson pins 7 and 9-15 of U9 will go low. Pins 14 and 15 of U9 are not used.The outputs at pins 7 and 9-13 of U9 are control signals which controlthe operation of various latches and two digital/analog converters, asdescribed in more detail below. The signal from pin 7 of U9 on a line2516 is a first row control signal, hereinafter designated FRC. Thesignal from pin 8 of U9 on line 2518 is a last row control signal,hereinafter designated LRC. The signal from pin 10 of U9 on line 2520 isa first column control signal, hereinafter designated FCC and the signalfrom pin 11 of U9 on line 2522 is a last column control signal,hereinafter designated LCC. The output from pin 12 of U9 on line 2524 isa first digital/analog control signal hereinafter designated ADACS,while the output from pin 13 of U9 on line 2526 is a seconddigital/analog control signal hereinafter designated BDACS.

The memory read/write signal, R/W, fed by the computer to line 6 of theJ1 connector of the mother board, is passed to pin 11 of U8B, part ofthe aforementioned 74LS244 integrated circuit U8. The correspondingoutput from pin 9 of U8B is fed to a line 2528 to provide an amplifiedmemory read/write signal, the uses of which will be described below. Theoutput from pin 9 of U8B is also fed to pin 1 of U10, which is acommerically-available 74LS640 bi-directional buffer. As those skilledin the art are aware, pin 1 of the 74LS640 controls the read/writedirection, and thus the read/write direction of U10 is controlled by thememory read/write signal R/W from the computer.

The clock signal φ2 from line J of the J1 connector is fed to pin 13 ofU8C, a further part of the aforementioned 74LS244 integrated circuit U8.The corresponding output from pin 7 of U8C is placed on the line 2514which, as already mentioned, is connected to pin 6 of U9. The outputfrom pin 7 of U8C is also fed to a line 2530, for purposes which will bedescribed below, and to pin 2 of U11A. U11 is a commercially-available74LS00 Schottky quadruple 2-input NAND gate. To provide the other inputto the gate U11A, the signal on line 2506 (which, as already described,is the signal indicating that the hexadecimal digit on lines A12-A15 ofthe address bus had a preselected value indicating that the address isone which affects the video-computer interface) is fed to pin 1 of U1B,a further part of the 74LS04 inverter U1 already described, and thecorresponding output from pin 2 of U1B is fed to pin 1 of U11A. U11 isprovided with the conventional power connections of pins 14 and 7. Theoutput from pin 3 of U11A is fed to pin 19 (the enable pin) of U10. Itwill be apparent to those skilled in the art that the effect theconnections established by U8C, U1B and U11A is that U10 is only enabledwhen the most significant hexadecimal digit on the address bus has thepreselected value and the clock signal φ2 is positive.

U10 is provided with conventional power connections at pins 20 and 10,while pins 18-11 of U10 are connected to lines D0-D7 respectively of thedata bus (lines D0-D7 are lines 31, 29, K, H, 32, 30, L and Jrespectively of the aforementioned J1 connector of the mother board.)The signals from pins 2-9 of U10 (corresponding to the signals at pins18-11 respectively) are placed on lines 0-7 of a buffered data bus 2532.Hereinafter for convenience, line 0 of bus 2532 will be referred to asline 2532-0 etc., and similarly for other buses.

It will be apparent to those skilled in the art that the effect of thecircuitry just described is that incoming signals from the computer databus are only transmitted to the bus 2532 when the most significanthexadecimal digit simultaeously appearing on lines A12-A15 of theaddress bus indicates that the signal is one intended for thevideo-computer interface, when the clock signal φ2 is positive and whenthe read/write signal R/W indicates that writing to the memory of thevideo-computer interface is intended. Similarly, transmission of datafrom the bus 2532 to the computer data bus will only occur when thepreselected most significant hexadecimal digit appears on the addressbus, the memory read/write signal is negative and the clock signal φ2 ispositive.

FIG. 46 shows circuitry which corresponds in substance to the rowcontrol portion 140C of the controller board 140 shown in FIG. 5. Asshown in FIG. 46, lines 2532-7 to 2532-0 of the buffered data bus 2532are connected to pins 18, 17, 14, 13, 8, 7, 4 and 3 respectively of eachof a pair of integrated circuits U12 and U13. U12 and U13 are each anoctal D-type latch of the commercially-available 74LS373 type, and areeach provided with conventional power connections at pins 20 and 10. U12and U13 both have pin 1 (output enable) grounded. To provide a latchenable signal to U12, the FRC signal from pin 7 of U9 (FIG. 45)appearing on line 2516 is fed to pin 5 of U14A. Integrated circuit U14is a hex inverter of the commercially-available 74LS04 type. Theinverted output from pin 6 of U14A is passed to pin 11 of U12.Similarly, the LRC signal from pin 8 of U9 (FIG. 45) appearing on line2518 is fed to pin 9 of U14B, a further part of the same U14 integratedcircuit, and the corresponding inverted output from pin 8 of U14B is fedto pin 11 of U13.

U12 serves as a first row latch. As will be apparent to those skilled inthe art, when the address on the computer address bus is that specifyingthat the data on the data bus represents a value of the first row of the"window" from which video data is to be retained, the output from pin 7of U9 goes low, so that the latch enable function at pin 11 of U12 goeshigh and U12 thus latches to the 8-bit value simultaneously appearing onthe buffered data bus 2532. Thus, U12 serves to store the 8-bit firstrow value of the window. U13 operates in an exactly similar manner,except that it is a last row latch and serves to store the value of thelast row of the window.

The outputs at pins 19, 16, 15 and 12 of U12 (which correspond to thesignals originally received at pins 18, 17, 14 and 13 respectively, andwhich represent the four most significant bits of the 8-bit first rowvalue) are fed to pins 9, 10, 1 and 15 respectively of an integratedcircuit U15. Similarly, the outputs from pins 9, 6, 5 and 2 of U12(which correspond to the inputs of pins 8, 7, 4 and 3 respectively ofU12 and specify the four least significant bits of the first row value)are fed to pins 9, 10, 1 and 15 respectively of U16. Integrated circuitsU15 and U16 are each a commerically-available 74LS191 synchronousup/down 4-bit counter. These two four-bit counters are interconnected sothat they function in effect as an 8-bit counter, pin 13 (the rippleclock output) of U16 being connected to pin 4 of U15. Both U15 and U16are provided with conventional power connections at pins 16 and 8. Also,both U15 and U16 have their down/up input, pin 5, connected via aresistor R203 to a +5V supply line, thereby locking them in thedown-counting mode. Pin 11 on both U15 and U16, the load input, receivesthe vertical synchronization signal, VSYNCH, from a line 2534; themanner in which the signal is placed on the line 2534 will be describedbelow. Pin 14 on both U15 and U16 receives the half-speed horizontalsynchronization signal, SBLNK/2 from a line 2536; the manner in whichthis signal is generated will be described below. Finally, pin 4 of U16is grounded. The max/min output from pin 12 of U15 is taken to pin 13 ofa NAND gate U17A. U17 is a Schottky quadruple 2-input NAND gate of thecommercially-available 74LS00 type. Similarly, the max/min output frompin 12 of U16 is fed to pin 12 of U17A.

As will be apparent to those skilled in the art, U15, U16 and U17A serveas an 8-bit first row counter and at the beginning of each frame, theVSYNC signal from line 2534 causes the 8-bit first row value latched inU12 to be loaded into U15 and U16, the four most significant bits goingto U15 and the four least significant bits going to U16. Thereafter, theSBLNK/2 signal from line 2536 causes the 8-bit first row value thusloaded to be decremented when each new line of data is begun (as alreadyexplained, it is necessary to divide the frequency of the horizontalsynchronization signal by 2 in order to overcome the effect ofinterlacing when the preferred TN2500 video camera is employed). Afterthe desired number of lines have passed, the outputs at pins 12 of U15and U16 go high simultaneously, thereby causing the output at pin 11 ofU17A to go low. Thus, the output at pin 11 of U17A only goes low whenthe first line of the window to which video data is to be stored hasbeen reached.

Generation of an appropriate signal when the last row of the videowindow has been reached is accomplished in a generally similar manner.The outputs at pins 19, 16, 15 and 12 of U13 (which correspond to theinputs of pins 18, 17, 14 and 13 respectively thereof, and which definethe four most significant bits of the last row value latched in U13) arefed to pins 9, 10, 1 and 15 respectively of U18, while the outputs frompins 9, 6, 5 and 2 of U13 (which correspond to the inputs at pins 8, 7,4 and 3 respectively, and which represent the four least significantbits of the last row value latched in U13) are fed to pins 9, 10, 1 and15 respectively of U19. Integrated circuits U18 and U19 are each 4-bitcounters of the commercially-available 74LS191 type. The remainingconnections to U18 and U19 are exactly similar to those to U15 and U16respectively. Thus, each of U18 and U19 has its pin 5 connected to the+5V supply line via resistor R203, its pin 11 connected to the line 2534and its pin 14 connected to the line 2536. Conventional powerconnections are made to U15 and U19 at pins 16 and 8 on each chip, pin 4of U19 is grounded, and pin 13 of U19 and pin 4 of U18 areinterconnected.

It will be apparent to those skilled in the art that the operation ofU18 and U19 is exactly parallel to that of U15 and U16. At the beginningof each frame, the VSYNC signal from line 2534 causes loading of the8-bits of the last row value latched in U13 into U18 and U19, andthereafter the SBLNK/2 signal from line 2536 causes the 8-bit value thusloaded to be decremented each time a new line of video data is begun.Accordingly, when the appropriate number of lines has elapsed, theripple clock output at pin 13 of U18 goes low, thus signalling the endof the window. It is now necessary to process the outputs from U17A andfrom pin 13 to U18 in order to generate both an end-of-frame signal,EOF, which will signify the acquisition of video date by the interface,and to gate the signals indicating the rows to be accepted in a mannerdependent upon the row skip function, in order that lines of video datamay be skipped when the instructions set by the operator on the computerrequire this. Generation of the EOF signal is accomplished by anintegrated circuit U20 which is a dual J-K positive-edge triggeredflip-flop of the commercially-available 74LS109 type. The ripple clocksignal from pin 13 of U18 is fed directly to pins 3 and 13 (the two Kinputs of the two flip-flops on U20). The same ripple clock signal frompin 13 of U18 is also passed to pin 5 of U21A. Integrated circuit U21 isa Schottky quadruple 2-input NOR gate of the commercially available74LS02 type. Pin 6 of U21A is grounded so that U21A acts an inverter theoutput from pin 4 of U21A is fed to pin 3 of U21B, a further NOR gate onintegrated circuit U21. Pin 2 of U21B receives the output from pin 11 ofU17A, and the output from pin 1 of U21B is fed to pin 14 (the J2 input)of U20. Pins 4 and 12 (the two CP inputs) of U20 receive the SBLNK/2signal from line 2536, while pins 1 and 11 the (C1 and S2 inputsrespectively) of U20 are held positive, being connected to the +5Vsupply line via a resistor R204. U20 receives the conventional powerconnections at pins 16 and 8, and its pin 2 (J1 input) is grounded. Pins5 and 15 of U20 (the S1 and C2 inputs respectively) receive the VSYNCsignal from line 2534. Pin 6 (the Q1 output) of U20 provides the EOFsignal on a line 2538. The use of this signal will be described below.

Although the exact operation of U20 and its associated circuitry issomewhat complex, it will be apparent to those skilled in the art thatthe EOF signal on line 2538 will only begin to be generated after U20has received a pulse indicating the beginning of a frame (i.e. after theoutput from U17A indicates that the beginning of the window has beenreached) and will terminate when the output from pin 13 of U18 indicatesthat the end of the window has been reached. Thus, the EOF signal online 2538 indicates passage through the window for which video data isto be generated, in the same manner as the corresponding signal shown inFIG. 14 above.

The row skipping function is handled by an integrated circuit U22, whichis a synchronous 4-bit up/down binary counter of thecommercially-available 74LS169 type. U22 has conventional powerconnections at pins 16 and 8. Pin 1 is grounded (thereby locking thecounter in the down-counting mode) and pin 7 is also grounded, therebyholding the enable P function permanently low. Pin 2 of U22 (the CPinput) receives the SBLNK/2 signal from line 2536, while pins 3, 4, 5and 6 are connected to lines 0, 1, 2 and 3 respectively of a four-linebus 2540. This bus 2540 carries a four-bit signal representing the rowskip function; the manner in which the signals are placed on the bus2540 will be described below. Pin 10 of U22 (the enable T input) of U22receives the Q2 signal from pin 9 of U20, thereby ensuring that U22 onlycounts while the video signal is within the window defined by the firstand last row counts latched in U12 and U13 respectively.

The ripple counter output from pin 15 of U22 is fed to pin 9 of U17B, afurther NAND gate on the 74LS00 integrated circuit U17 mentioned above.U17B has the conventional power connections at pins 14 and 7. The otherinput to U17B at pin 10 thereof is derived from pin 11 of U17A. Theoutput from pin 8 of U17B is fed to pin 9 of U3B, a second inverter onthe integrated circuit U3 mentioned above. The inverted output from pin8 of U3B is fed to pin 9 (the load input) of U22.

It is believed that the mode of operation at U22 will be apparent tothose skilled in the art. U22 is not operational until the first line ofthe window has been reached. When the input from pin 11 of U17A to pin10 of U17B goes low, the output at pin 8 of U17B goes high, the outputat pin 8 of U3B goes low, and the low input at pin 9 of U22 causesloading of a 4-bit row skip value into U22. U22 then counts down at arate determined by the signal SBLNK/2 on line 2536 (i.e. U22 counts newlines of video data) until its counter reaches 0. When the counterreaches 0, the output at pin 15 of U22 goes low, and since both inputsto U17B are now low, its output changes. Once the ripple clock pulsefrom pin 15 of U22 is ended, the output of U17B changes and thesuccessive countdown cycles of U22 are repeated until the last line ofthe video window is reached. Once the last line has been reached, theinput at pin 10 of U22 goes high, thus terminating the operation of U22.

The output from pin 8 of U17B is also fed to pin 9 of U6B, which is asecond 4-input NAND gate on the 74LS04 integrated circuit U6 previouslymentioned. Pin U13 of U6B is held high, being connected to the +5Vsupply line via a resistor R205. Pin 12 of U6B receives the inverse ofthe half-speed horizontal synchronization signal (i.e. the inverse ofSBLNK/2) from a line 2542, while pin 10 of U6B receives the horizontalblanking signal SBLNK from a line 2544. The manner in which theappropriate signals are placed on the lines 2542 and 2544 will bedescribed below. Obviously, the action of U6B is to gate the output frompin 8 of U17B by both the SBLNK line signal and the inverse half speedhorizontal synchronization signal. The output from pin 8 of U6B on aline 2546 is the accept row signal, ACCROW.

FIG. 47 shows column control circuitry which functions in the samemanner as the column control portion 140B of the controller board 140shown in FIG. 5. In general, the column control circuitry shown in FIG.47 functions in a manner very similar to that of the row controlcircuitry shown in FIG. 46 except of course that the appropriatecounting circuits have to be reset by the half-speed horizontalsynchronization signal, not by the vertical synchronization signal, andthat the counters must count pixels not lines, so that the counterscount using the pixel-counting signal ERC, not the half-speed horizontalsynchronization signal.

As shown in FIG. 47, signals from lines 0-7 of buffered data bus 2532are fed to pins 3, 4, 7, 8, 13, 14, 17 and 18 respectively of each oftwo integrated circuits U23 and U24, which are each octal D-type latchesof the commercially-available 74LS373 type. U23 and U24 receive theconventional power connections at pins 20 and 10 and each have pin 1(output enable) grounded. The FCC output from pin 10 of U9 on line 2520(FIG. 45) is, as shown in FIG. 47, fed to pin 1 of U3C, which is a thirdinverter on the aforementioned 74LS04 integrated circuit U3. Theinverted output from pin 2 of U3C is fed to pin 11 (the latch enableinput) of U23. Similarly, the LCC from pin 11 of U9 on line 2522 (FIG.45) is, as shown in FIG. 47, fed to pin 3 of U3D, which is a fourthinverter on the aforementioned 74LS04 integrated circuit U3. As shown inFIG. 47, integrated circuit U3 receives the conventional powerconnections at pins 14 and 7. The inverted output from pin 4 of U3D isfed to pin 11 (the latch enable input) of U24.

As will be apparent to those skilled in the art, U23 functions as afirst column latch loading an 8-bit first column value from bus 2532when the signal from pin 10 of U9 indicates that the value on the bufferdata bus 2532 represents a first column value. Similarly, U24 acts as alast column latch loading an 8-bit last column value when the outputfrom pin 11 of U9 indicates that the signal on the data bus represents alast column value.

First column counting is effected by a pair of integrated circuits U25and U26 which function in a manner very similar to the first rowcounting action of integrated circuits U15 and U16 described above. U25and U26 are each a 4-bit synchronous up/down binary counter of thecommerically-available 74LS191 type, and the two integrated circuitsinterconnected so as to act, in effect, as a single 8-bit counter. Theoutputs from pins 19, 18, 15 and 12 of U23 (representing the four mostsignificant bits of the 8-bit first column value latched in U23) are fedto pins 9, 10, 1 and 15 respectively of U25, while the output from pins9, 6, 5 and 2 respectively of U23 (respresenting the four leastsignificant bits of the 8-bit first column value latched in U23) are fedto pins 9, 10, 1 and 15 respectively at U26. U25 and U26 receive theconventional power connections at pins 16 and 8, the inverse half-speedhorizontal synchronization signal at pin 11 (the load input) and theelement rate clock or pixel counting signal ERC from a line 2548 at pin14 (the clock input). Pin 5 (the down/up input) of each of U25 and U26is connected to a +5V supply line via a resistor R206, thereby lockingU25 and U26 in the down-counting mode. The ripple clock output from pin13 of U26 is fed to pin 4 (the enable input) of U25. Pin 4 (the enableinput) of U26 receives the accept row signal ACCROW from line 2546.

As will be apparent to those skilled in the art, when ACCROW goesnegative, U26 is enabled. As soon as the inverse half-speed horizontalsynchronization signal from line 2542 goes negative, U26 loads the fourleast significant bits of the 8-bit first row value latched in U23. U26then proceeds to decrement this 4-bit number once for every pixelscanned, using the ERC signal from line 2548. After U26 has counted downto zero, its ripple clock output at pin 13 goes negative, therebyenabling U25 since the inverse half-speed synchronization signal willstill have the same value (obviously U26 will count to zero in less thanone line of video data). U25 proceeds to load the four most significantbits of the 8-bit first column value latched in U23. Thereafter, U26goes through a number of countdown cycles and at the end of each cycleU25 decrements its counter value by 1. Obviously, when a number ofpixels corresponding to the pre-selected first column value latched inU23 have elapsed, both U25 and U26 will count down to zerosimultaneously, and both their max/min outputs at pin 12 will go highsimultaneously. The signal from pin 12 of U25 is fed to pin 9 of U27A,while the signal from pin 12 of U26 is fed to pin 11 of U27A. Pin 10 ofU27A receives the inverse half-speed horizontal synchronization signalfrom line 2542. U27 is a Schottky triple 3-input NAND gate of thecommercially-available 74LS10 type. As will be apparent to those skilledin the art, the output of U27A at pin 8 thereof will only go low whenthe ACCROW signal is negative (i.e. the line is to be accepted),counters U25 and U26 have counted a number of pixels equal to the firstcolumn value latched in U23 and the inverse half-speed horizontalsynchronization signal on line 2542 is positive (i.e. the linerepresented by the incoming video signal is a new line of video data,not a repeated line).

Last column counting is handled by two integrated circuits U28 and U29,which are each of the aforementioned 74LS191 type. The output at pins19, 16, 15 and 12 of U24 are fed to pins 9, 10, 1 and 15 respectively ofU28, while the outputs at pins 9, 6, 5 and 2 of U24 are fed to pins 9,10, 1 and 15 of U29. Pin 4 (the enable input) of U29 receives the ACCROWsignal from line 2546. Pin 11 on both U28 and U29 receives the inversehalf-speed horizontal synchronization signal from the line 2542, pin 5on U28 and U29 is connected to the +5V supply line via resistor R206 andpin 14 on U28 and U29 receives the ERC signal from line 2548. U28 andU29 are each provided with the conventional power connections at pins 16and 18, and the ripple counter output at pin 13 of U29 is conencted topin 4 (the enable input) of U28. For reasons which will be apparent tothose skilled in the art from the foregoing description of the operationof U18, U19, U25 and U26, the ripple clock output on pin 13 of U28 willonly go low when U28 and U29 have counted a number of pixels equal tothe last column value latched in U24.

The ripple clock output from pin 13 of U28 is fed to pin 9 of U21B whichis a further NOR gate on the 74LS02 integrated circuit U21 previouslymentioned. U21B receives the conventional power connections at pins 14and 7 and its pin 8 (second input) is grounded so that U21B acts as aninverter. The output from pin 10 of U21B is fed to pin 11 of U21C, athird NOR gate on the same 74LS02 integrated circuit U21. Pin 12 (thesecond input) of U21C receives the output from pin 8 of U27A. The outputat pin 13 of U21C is fed to pin 2 (the J1 input) of U30A. Integratedcircuit U30 is a positive edge-triggered dual J-K flip-flop of thecommercially-available 74LS109 type. U30A serves substantially the samefunction in the column control circuitry as the similar integratedcircuit U20 serves in the row control circuitry. However, since there isno need for the column control circuitry to generate any signalanalogous to the EOF signal generated by integrated circuit U20 in therow control circuitry, only one of the flip-flop on U30 is used in thecolumn control circuitry. Pin 1 (the C1 input) of U30A receives theinverse half-speed horizontal synchronization signal from line 2542, pin4 (the CP1 input) of U30A receives the ERC signal from line 2548, andpin 3 (the K1 input) of U30A receives the ripple counter output from pin13 of U28. U30A is provided with the conventional power connections atpins 16 and 8, and its pin 5 (the S1 input) is also connected to the +5Vsupply line via a resistor R208. The Q1 output at pin 7 of U30A is fedto pin 10 (the enable T input) of an integrated circuit U31. Integratedcircuit U31 is a synchronous 4-bit up/down counter of thecommercially-available 74LS169 type and functions as a column skipcounter in substantially the same manner as the integrated circuit U22described above functions as a row skip counter. Pin 2 (the CP input) ofU31 receives the ERC signal from line 2548, while pins 6, 5, 4 and 3 ofU31 (the four data inputs) are connected to lines 3, 2, 1 and 0respectively of a bus 2550, which carries a 4-bit number defining thecolumn skip function. The manner in which the column skip function isplaced on bus 2550 will be described below. U31 receives theconventional power connections at pins 16 and 8, pin 1 is grounded tolock U31 in the down-counting mode, and pin 7 is also grounded so thatthe enable P function of U31 is always enabled.

The ripple carry output from pin 15 of U31 is fed to pin 5 of U17C, athird NAND gate on the integrated circuit U17 previously mentioned. Thesecond input to pin 4 of U17C is supplied from pin 8 of U27A. The outputat pin 6 of U17C is the accept pixel signal, ACCPIX, which is placed ona line 2552 for purposes to be described below. The output from pin 6 ofU17C is also supplied to pin 5 of U3E, a further inverter on the 74LS04integrated circuit U3 previously mentioned. The inverted output from pin6 of U3E is fed to pin 9 (the load input) of U31.

It will be apparent to those skilled in the art that the circuitry justdescribed causes U31 to operated in a manner substantially analogous toU22. U31 is only enabled at pin 10 when the row and column numbers ofthe incoming video data relate to the desired window. When the videodata relate to this window, U31 goes through successive cycles ofloading the column skip function from bus 2550, counting down to zeroand, upon reaching zero, outputing a ripple carry output pulse from pin15. Thus, U31 serves to gate the accept pixel signal ACCPIX inaccordance with the column skip function previously set by the operator.

The circuitry shown in FIG. 48 serves to multiplex signals from thecomputer with signals from the camera and to handle communications withthe memories in the video computer interface. Although the detailedlayout is somewhat different, the circuitry shown in FIG. 48 correspondslargely to the PIA/VIA SELECT, computer communication portion 140A ofthe controller board 140 and the memory control portion 274A of thememory board 274 shown in FIG. 5.

The circuitry shown in the upper left-hand part of FIG. 48 isresponsible for handling and modifying various signals from the videocamera to produce signals used by other parts of the video-computerinterface. The horizontal synchronization signal, SBLNK from the videocamera (this signal appears on line 20 of the J2 connector of the AIM-65mother board) is fed to pin 13 of U7C, a third AND gate on the 74LS08integrated circuit U7 mentioned above. The second input to U7C at pin12, is held high, being connected to a +5V supply line via a resistorR210, so that U7C functions as an amplifier. The output from pin 11 ofU7C is fed to pin 12 (the CP2 input) of U30B, which is the secondflip-flop of the 74LS109 integrated circuit U30 already mentioned. U30Breceives the conventional power connections at pins 16 and 8. Pins 11and 14 (the S2 and J2 inputs respectively) are held high, beingconnected to the +5V supply line via resistor R210. Pin 13 (the K2input) of U30B is grounded.

The vertical synchronization signal, VSYNC, from line 24 of the J2connector of the AIM-65 mother board, is fed to pin 9 of U1C, a furtherinverter on the 74LS04 integrated circuit U1 already mentioned. Thecorresponding inverted input from pin 8 of U1C, the inverse verticalsynchronization signal, VSYNC or CLR, is placed on the line 2534 alreadymentioned, and is also fed to pin 15 (the C2 input) of U30B. The Q2output from at pin 10 of U30B is the half-speed horizontalsynchronization signal SBLNK/2, which is placed on the line 2536 alreadymentioned, while the Q2 output at pin 9 of U30B is of course the inversehalf-speed horizontal synchronization signal, which is placed on theline 2542 already mentioned. The ERC signal from the video camera,appearing at line 11 of the of J2 connector of the AIM-65 mother board,is fed via a resistor R212 to the mid-point of a voltage dividercomprising two identical resistors R214 and R216 connected in seriesbetween the +5V supply line and ground, and thence to pin 17 of U8C, afurther part of the 74LS244 buffer/line driver integrated circuit U8already mentioned. The corresponding output, at pin 3 of U8C, which issimply an amplified version of ERC, is placed on the line 2548 alreadydescribed. The output from pin 3 of U8A is also fed to pin 13 of U3F, asixth inverter on the 74LS04 integrated circuit U3 already described.The corresponding inverse signal ERC, appearing at pin 12 of U3F, isplaced on a line 2554; the use made of this signal will be describedbelow.

The remainder of the circuitry in FIG. 48 is mainly concerned withmultiplexing signals from the buffered computer data bus and from acamera data bus and supplying the multiplexed signals to the memories ofthe computer interface. Lines 0-7 of buffered data bus 2532 (fromintegrated circuit U10 shown in FIG. 45) are fed to pins 33-26respectively of integrated circuit U33, which is an R6522 input/outputport manufactured by Rockwell International Corporation. As previouslymentioned, further details of this device may be obtained by referenceto Document No. 2900D47 Revision 1, published in Oct. 1978 by RockwellInternational Corporation. U33 serves as a multiple latch to storevarious parameters sent from the computer and required by thevideo-computer interface, and also handles various communications withthe video camera and the computer. U33 is provided with the conventionalpower connection at pins 20 and 1. Its pin 24 (the CS1 input) is heldhigh, being connected via a resistor R218 to the +5V supply line. Pin 23(the CS2 input) of U33 receives the CSA signal on line 2510 from pin 7of U5 (as previously described with reference to FIG. 45). Pins 5, 4, 3and 2 (outputs PA3-PA0 respectively) of U33 are connected to lines 3-0respectively of bus 2540 which, as already described, serves to transmitthe 4-bit value of the row skip function to U22 (FIG. 46). Similarly,pins 9-6 (outputs PA7-PA4) of U33 are connected to lines 3-0respectively of bus 2550, which, as already described, serves totransmit the 4-bit value of the column skip function to U31 (FIG. 47).

Pin 21 of U33 serves to carry the IRQ output from the video computerinterface to the computer and is connected to line D of the J1 connectorof the mother board. Pins 19 and 16 (inputs CB2 and PB6 respectively ofU33) receive the inverted vertical synchronization signal, VSYNC frompin 8 of U1C. Pins 18 and 17 (the CB1 and PB7 inputs respectively) ofU33 receive the EOF signal from line 2538. As already described, thisEOF signal is generated at pin 6 of U20 (see FIG. 46). Pins 35-38(inputs RS3-RS0 respectively) of U33 are connected to pins 18, 16, 14and 12 respectively of U8A (FIG. 45) and thus receive the four leastsignificant bits from the computer address bus, appropriately bufferedby U8A. Pin 34 of U33 receives a reset signal, RES, from line 5 of theJ1 connector of the mother board. Pin 22 of U33 receives the read/writesignal R/W from line 2528 which, as already described, is connected topin 9 of U8B (FIG. 45). Pin 25 of U33 receives the clock signal φ2 fromline 2530 which, as already mentioned, is connected to pin 7 of U8C(FIG. 45).

Pin 15 (the PB5 output) of U33 is connected to pin 3 of U14C, which is athird inverter on the 74LS04 integrated circuit U14 already mentioned.The inverted signal from pin 4 of U14C is fed to line 1 of the J2connector of the mother board, and serves as an automatic gain controlsignal for the video camera. Pin 14 (the PB4 output) of U33 is connectedto line 23 of the J2 connector, while pin 13 (the PB3 output) of U33 isfed to pin 11 of U14D (a fourth inverter on the 74LS04 integratedcircuit U14 already mentioned) and the inverted output from pin 10 ofU14D is fed to line 22 of the J2 connector. Lines 22 and 23 of the J2connector furnish mode control signals to the video camera, the signalon line 22 being the I/244 and that on line 23 being the N/122 signal.The use which is made of these signals by the TN2500 video camera willbe known to those familiar with this camera.

Pin 12 of U33 is not used. Pin 11 (the PB1 output) is connected to line6 of the J2 connector, which serves to transmit the IIG signal to thecamera. It will be seen from FIG. 48 that lines 9 and 21 of the J2connector are not used and are simply grounded. Pin 10 (the PB0 output)of U33 provides the camera control signal, COM/CAM, which, as alreadydescribed, indicates when the camera is to furnish video data. ThisCOM/CAM signal is placed on a line 2556 for purposes which will bedescribed later.

The actual multiplexing of the computer data bus and camera data bussignals is effected by a pair of integrated circuits U34 and U35.Integrated circuit U34 is an octal bus transceiver of thecommercially-available 74LS245 type, while integrated circuit U35 is aninverting buffer/line driver of the commercially-available 74LS244 type.U34 handles signals to and from the bus 2532, these being (as alreadydescribed) signals from the computer data bus buffered by U10. U35handles signals from the camera data bus 306. U34 and U35 areinterconnected so that only one of them is enabled at any one time.

Pins 11-18 of U34 receive the signals from lines 7-0 respectively of bus2532. U34 is provided with the conventional power connections at pins 20and 10. Pin 1 (the direction pin) of U34 receives the read/write signalR/W from line 2528. To provide the enable input to pin 19 of U34, theCOM/CAM signal on line 2556 is fed to pin 5 of U11B, a second NAND gateon the integrated circuit U11 previously mentioned. The second input toU11B, at pin 4 thereof, is the memory enable signal, MI, from line 2512;as already mentioned, the MI signal is supplied from U7A (FIG. 45). Theoutput at pin 6 of U11B is supplied to the enable input, pin 19, of U34.Pins 9-2 of U34 are connected to lines 7-0 respectively of a memory bus2558.

Lines 7-0 of camera data bus 306 (appearing on lines 12, 10, 5, 7, 2, 3,4 and 8 respectively of the J2 connector of the mother board) are fed topins 8-1 respectively of a resistor assembly RA1. Assembly RA1 is anAllen-Bradley 316B resistor assembly and comprises eight parallel 100ohm resistors. The outputs on pins 9-16 of RA1 (which correspond to theinputs on pins 8-1 respectively) are fed to pins 8, 6, 4, 2, 11, 13, 15and 17 respectively of U35 and are also fed to pins 2-9 respectively ofa resistor assembly RA2, which is an Allen-Bradley 310 type 10-pin SIPassembly. As is well known to those skilled in the art, this assembly,which has pin 1 connected to the +5V supply line and pin 10 grounded,comprises eight series pairs of 22 Kohm resistors connected in parallel,and the inputs on pins 2-9 are connected to the midpoint of the voltagedividers formed by these pairs of resistors, as shown in FIG. 48.Assemblies RA1 and RA2 are provided for impedance matching of the cameracable which terminates in bus 306.

U35 is provided with the conventional power connections to pins 20 and10. Pins 1 and 19 (the two enable inputs) of U35 receive the COM/CAMsignal from line 2556. Pins 12, 14, 16, 18, 9, 7, 5 and 3 of U35 areconnected to lines 7-0 respectively of memory bus 2558.

It is believed that the mode of operation of U34 and U35 will be readilyapparent to those skilled in the art. Obviously, when the COM/CAM signalgoes low, U35 is enabled and signals from the camera data bus 306 willbe sent to the memory bus 2558. The control of U34 is somewhat morecomplicated since U34 may be required to transmit data in bothdirections between the bus 2532 and the memory bus 2558. (The ability totransmit data from the computer to the interface memories is notstrictly necessary in the present form of the interface. However, thisfacility may be useful for testing purposes and is also provided sinceit may be useful in further developments of the interface.) U34 is onlyenabled when the input at pin 19 thereof goes low which, because ofU11B, is only achieved when both the memory enable signal MI and COM/CAMgo high; the gating of the high COM/CAM signal with by the signal MIeffected by U11B is necessary to ensure that U34 is not enabled when theaddress appearing on the computer address bus is one of the reservedaddresses which is intended for a function of the video computerinterface other than writing into the memories. Once U34 has beenenabled by a high COM/CAM and a high MI , the direction of transmissiontherethrough depends upon the value of the signal R/W fed to pin 1thereof; when R/W is high, data will be transmitted from the memory bus2558 to the bus 2532, while when R/W goes low, data will be transmittedfrom the bus 2532 to the memory bus 2558.

FIG. 49 shows the memories of the video computer interface, togetherwith associated circuitry used for generating addresses in the memoryand for various control functions. As will be apparent to those skilledin the art, as 8-bit numbers representing video data from acceptedpixels are fed to the video-computer interface when the computerinstructs the interface to acquire video data from the camera, it isnecessary to generate addresses to advise the memory of the variouslocations in which the incoming video data should be stored. Generationof the necessary addresses is effected by three integrated circuits U36,U37 and U38, each of which is a synchronous 4-bit counter of thecommercially-available 74LS161 type. U36, U37 and U38 are interconnectedso as to generate the 12-bit addresses required by the 4K memorydescribed below. Each of U36, U37 and U38 is provided with conventionalpower connections at pins 16 and 8. Pins 3, 4, 5 and 6 of each of U36,U37 and U38 (the four data inputs of each counter) are all held high,being connected to the +5V supply line via a resistor R220. Pin 1 (theclear input) of each of U36, U37 and U38 receives the VSYNC signal fromline 2534 in order to ensure that all three counters are zeroed at thebeginning of each frame of video data. Pin 9 (the load input) of each ofU36, U37 and U38 is held high, being connected to the +5V supply linevia the aforementioned resistor R220. To provide the clock input to U36,U37 and U38, the ERC signal on line 2554 (from pin 12 of U3F (FIG. 48)is fed to pin 2 of U27B, a second NAND gate on the 74LS10 integratedcircuit U27 already mentioned. Pin 1 of U27B receives the ACCPIX signalon line 2552 from pin 6 of U17C (FIG. 47). The third input to U27B, atpin 13 thereof, is the inverse of COM/CAM signal generated by passingthe COM/CAM signal on line 2556 to pin 13 of U1D (a fourth inverter onthe 74LS04 integrated circuit U1 already mentioned) and passing thecorresponding inverted output from pin 12 of U1D to pin 13 of U27B. Theoutput from pin 12 of U27B is fed to pin 2 (the clock input) of each ofU36, U37 and U38. As will be apparent to those skilled in the art, theprovision of U27B ensures that the counters U36, U37 and U38 onlyactually count when the ERC and ACCPIX signals are high and the COM/CAMsignal is low i.e. when the computer has set the interface to acceptvideo data, the pixel from which video data is being received on thecamera data bus 306 is one of those selected by the operator forretention of video data and ERC is alternately high and low indicatingthat the camera is transmitting video data from a pixel. Pins 7 and 10of U38 (the two enable inputs) are held high, being connected to the +5Vsupply line via the resistor R220. The carry output from pin 15 of U38is fed to pin 7 (the enable P input) of each of U36 and U37. The carryoutput from pin 15 of U37 is fed to pin 10 (the enable T) input of U36.It will be apparent to those skilled in the art that the effect of theaforementioned interconnections is that U37 will only be enabled when acarry output is present at pin 15 of U35, and U36 will only be enabledwhen carry outputs are simultaneously present at pins 15 and 16 of U37and U38. Furthermore, it will be apparent to those skilled in the artthat, at the beginning of each frame of video data, U36, U37 and U38 areall reset by the VSYNC signal on line 2534 and that thereafter assuccessive pixels are accepted the 12-bit number represented by pins 11,12, 13 and 14 on each of U36, U37 and U38 will be incremented each timea pixel is accepted, provided that the computer has set the COM/CAMsignal low to order the interface to acquire video data.

The outputs from pins 11, 12, 13 and 14 of U36 (which represent the fourmost significant bits of the 12-bit address generated by U36, U37 andU38) are fed to pins 10, 13, 6 and 3 respectively of an integratedcircuit U39. Similarly, the outputs from pins 11, 12, 13 and 14 of U37are fed to pins 10, 13, 6 and 3 respectively of an integrated circuitU40 and the outputs from pins 11, 12, 13 and 14 of U38 are fed to pins10, 13, 6 and 3 respectively of an integrated circuit U41. U39, U40 andU41 are each a Schottky quadruple 2-input 3-state multiplexer of thecommercially-available 74LS257 type. U39, U40 and U41 are each providedwith conventional power connections at pins 16 and 8 and in all threeintegrated circuits pin 15 (the output control) is grounded. Pin 1 (theselect input) of each of U39, U40 and U41 is provided with the inverseCOM/CAM signal from pin 12 of U1D. Thus, when COM/CAM goes low (i.e.when the interface is instructed to acquire video data from the camera)the outputs of U39, U40 and U41 will track the inputs at pins 10, 13, 6,3 thereof.

Pins 11, 14, 5 and 2 of U39 receive the signals from lines A11-A8respectively of the computer address bus. Similarly, pins 11, 14, 5 and2 of U40 receive the signals from lines A7-A4 respectively of thecomputer address bus and pins 11, 14, 5, and 2 of U41 receive thesesignals from lines A3-A0 respectively of the computer address bus.Obviously, when COM/CAM goes high, the outputs from pins 9, 12, 7 and 4of each of U39, U40 and U41 will be determined by the three leastsignificant hexadecimal digits on the computer address bus, provided themost significant hexadecimal digit on the same bus has the pre-selectedvalue.

The output from pin 9 of U39 (which, when video data is being acquiredand thus the outputs from U39, U40 and U41 correspond to the inputsthereto from U36, U37 and U38 respectively, respresents the mostsignificant bit of the 12-bit address generated by U36, U37 and U38) isfed to pin 10 of U11C, which is a third NAND gate on the 74LS00integrated circuit U11 previously mentioned. The COM/CAM signal on line2556 is fed to pin 2 of U17D, a fourth NAND gate on the 74LS00integrated circuit U17 previously mentioned. The second input to pin 1of U17D is the signal DS on line 2504 from S101 (FIG. 45). The gating ofCOM/CAM by DS effected by U17D serves to prevent writing to memory whenthe address involved is one reserved for purposes other than writing tomemory. The output from pin 3 of U17D is fed to pin 9, the second input,of U11C. The output at pin 8 of U11C is fed to pin 18 (the CS input) ofan integrated circuit U42.

The output from pin 9 of U39 is also passed to pin 3 of U1E, a fifthinverter on the 74LS04 integrated circuit U1 already mentioned. Theinverted output at pin 4 of U1E is fed to pin 12 of U11D, a fourth NANDgate on the 74LS00 integrated circuit U11 already mentioned. Pin 13, thesecond input, of U11D is supplied with the output from pin 3 of U17D.The output from pin 11 of U11D is fed to pin 18 (the CS input) of anintegrated circuit U43.

U42 and U43 are each a 2K random access memory of type HM6116P2manufactured by Hitachi. Each of U42 and U43 is provided withconventional power connections at pins 24 and 12. It will be apparent tothose skilled in the art that the effect of U17D, U11C, U1E and U11D isthat when COM/CAM is low (i.e. when the computer is instructing theinterface to acquire video data from the camera) one or other, but notboth, of U42 and U43 can be enabled, depending upon the output from pin9 at U39 i.e. depending upon whether the most significant bit of the12-bit address generated by U36, U37 and U38 is a 1 or a 0.

In each of U42 and U43, pins 19, 22 and 23 receive the outputs from pins12, 7 and 4 respectively of U39. Similarly, pins 1-4 of U42 and U43receive the signals from lines 9, 12, 7 and 4 respectively of U40 andpins 5-8 of U42 and U43 are supplied with the signals from pins 9, 12, 7and 4 respectively of U41. Thus, when the interface is acquiring videodata, each of U42 and U43 is supplied with the 11 least significant bitsof the 12-bit address generated by U36, U37 and U38.

Pins 17, 16, 15, 14, 13, 11, 10 and 9 of U42 and U43 are connected tolines 7-0 respectively of the memory bus 2558. Pin 20 of U42 and U43supplied with the inverse COM/CAM signal from pin 12 of U1D.

The generation of the signal fed to pin 21 (the WE input) of U42 and U43is somewhat complex and is accomplished by circuitry shown in the bottomleft-hand part of FIG. 49. The R/W signal on line 2528 is fed to pin 11of U1F, a sixth inverter on the 74LS04 integrated circuit U1 previouslymentioned. As shown on U1F, U1 is provided with the conventional powerconnections at pins 14 and 7. The inverted output from pin 10 of U1F isfed to pin 4 of U27C, a third NAND gate on the 74LS10 integrated circuitU27 previously mentioned. The second input to pin 5 of U27C is the clocksignal φ2 from line 2530, while the third input to pin 3 of U27C is theCOM/CAM signal from line 2556. As shown in FIG. 49, integrated circuitU27 is provided with the conventional power connections at pins 14 and7. The output from pin 6 of U27C is fed to pin 5 of U7B, a second ANDgate on the 74LS08 integrated circuit U7 previously described. Thesecond input to pin 4 of U7B is the output from pin 12 of U27B.Integrated circuit U7 is provided with the conventional powerconnections at pins 14 and 7. The output from pin 6 of U7B is fed to pin21 of U42 and U43. Although this circuitry associated with pins 21 ofU42 and U43 is somewhat complex, it will be apparent to those skilled inthe art that the circuitry just described ensures that U42 and U43 areonly enabled when ACCPIX, ERC, COM/CAM, R/W and φ2 all have the correctvalues for writing into memories U42 and U43. It will also be apparentfrom the foregoing description that, when the interface is gatheringvideo data from the camera data bus 306, U42 and U43 make use of theaddresses generated by U36, U37 and U38, whereas when the computer isreceiving data from memories U42 and U43, these memories use theaddresses supplied to U39, U40 and U41 from lines A11-A0 of the computeraddress bus.

FIG. 50 shows the circuitry used to drive the osciloscope 76 shown inFIG. 4, and corresponds in substance to portion 280B of the board 280shown in FIG. 5. As shown in FIG. 50, lines 7-0 of buffered data bus2532 (derived from the outputs of integrated circuit U10, as shown inFIG. 45) are supplied to pins 8-1 respectively of each of a pair ofintegrated circuits U44 and U45. U44 and U45 are both digital analogconverters of type AD558, manufactured by Analog Devices, and are eachprovided with conventional power connections at pins 11 and 12. In bothU44 and U45, pins 13 and 14 are grounded, and are also connected to the+5V supply line via a capacitor (C101 for U44 and C102 for U45). Pin 10of U44 receives the ADACS control signal from line 2524 (from U9, pin12--see FIG. 45), while pin 10 of U45 receives the BDACS control signalfrom line 2546 (from U9 pin 13).

As shown in the lower part of FIG. G, the R/W signal on line 2528(derived from U8B, pin 9--see FIG. 45) is supplied to pin 1 (the A1input) of U46A. Integrated circuit U46 is a dual monostablemultivibrator of the commerically-available 74LS221 type provided withthe conventional power connections at pins 16 and 8. Pin 2 (the B1input) of U46A receives the clock signal φ2 from line 2530; aspreviously mentioned, this signal originates at pin 7 of U8C (FIG. 45).Pin 9 (the A2 input) of U46A is grounded, pin 3 (the first clear input)is connected to the +5V supply line via a resistor R222 and pin 15 isconnected to the same supply via a resistor R224. Pins 14 and 15 of R46Aare interconnected via a capacitor C104.

The Q1 output from pin 4 of U46A is fed to pin 40 of U46B, the secondmonostable multivibrator on the aforementioned 74LS221 integratedcircuit U46. Pin 11 (the second clear input) of U46B is connected to the+5V supply line via the resistor R222, pin 7 of U46B is connected to thesame supply line via a resistor R226 and pins 6 and 7 of U46B areinterconnected via a capacitor C106. The Q2 output from pin 12 of U46Bis supplied to pin 9 (the clear input) of each of U44 and U45.

Integrated circuit U46 serves to broaden the pulses received on lines2528 and 2530 in order to provide proper clear inputs to U44 and U45,since the duration of the pulses arriving on lines 2528 and 2530 may notbe sufficient to provide proper operation of U44 and U45.

The output from pin 15 of U44 is fed directly to a line 2560, whichprovides the first input to the double-trace oscilloscope 76 (shown inFIG. 4). Pin 16 of U44 is connected to line 2560 via a resistor R228.Similarly, pin 15 of U45 is connected directly to a line 2562, whichprovides the second input to the oscilloscope 76 (FIG. 4) and pin 16 ofU45 is connected to line 2562 via a resistor R230. As will be apparentto those skilled in the art, when the appropriate control signals arereceived on lines 2524 and 2526, U44 and U45 proceed to output to theoscilloscope 76 analog versions of the digital data arriving on the bus2532.

FIG. 51 shows the circuitry used to "highlight" the picture on the videomonitor 72 (FIG. 4) i.e. to modify the image displayed on the monitor soas to advise the operator which pixels have been selected for acceptanceof video data. The circuitry shown in FIG. 51 fulfills the same functionas the Summer 280C of the first video-computer interface previouslydescribed as shown in FIGS. 5 and 13B.

The first second and video inputs are fed to the J4 and J3 connectorsrespectively of the AIM-65 mother board and are then placed on lines2564 and 2566 respectively. (The preferred TN2500 video camera producesonly a single analog video output, which may be fed to either of thevideo inputs shown in FIG. 51. The second video input is provided sothat, if desired, a second image can be superimposed upon the image ofthe weld pool area seen on the monitor 72. For example, when thevideo-computer interface is carrying out the weld pool width measuringsoftware shown in FIGS. 15 and 17-17H, a graph of the light intensityalong the cursor could be superimposed on the image of the weld poolarea so that the operator may check that the local minima of lightintensity detected by the software correspond to the visually-observableedges of the weld pool). Line 2564 is connected to ground via a resistorR232 and is also connected via a capacitor C108, a fixed resistor R234and a variable resistor R236 all connected in series to pin 2 (thenegative input) of an integrated circuit U47, which is a type CA 3100Eanalog amplifier manufactured by RCA. Line 2566 is similarly connectedto ground via a resistor on R238 and is also connected via a capacitorC110, a fixed resistor R240 and a variable resistor R242, all connectedin series, to pin 2 of U47. Also, as shown in FIG. 51, the ACCPIX signalon line 2552 (from pin 6 of U17C--see FIG. 47) is fed via a fixedresistor R244 and a variable resistor R246 connected in series to pin 2of U47.

U47 receives the conventional power connections, +15V to pin 7 and -15Vto pin 4. Pins 7 and 4 are also connected to ground via capacitors C112and C114 respectively. Pins 1 and 8 of U47 are bridged by a capacitorC116 and pin 3 (the positive input) of U47 is grounded via a resistorR248. To provide feedback for amplifier U47, the output from pin 6 ofU47 is fed via an RC circuit (comprising a capacitor C118 and resistorR250 connected in parallel) to pin 2 of U47. The output from pin 6 ofU47 is also fed via a resistor R252 to pin 2 (the negative input) ofU48, which is a second type CA 3100E analog amplifier. Pin 3 (thepositive input) of U48 is grounded via a resistor R254, pins 1 and 8 ofU48 are interconnected via a capacitor C120, pins 7 and 4 of U48 receivethe conventional +15V and -15V respectively power inputs, pins 7 and 4also being connected to ground via capacitors C122 and C124respectively. The output from pin 6 of U48 is fed via resistor R256 tothe base of an NPN transistor Q100, which is of thecommerically-available LN2222 type. A resistor R258 and a capacitor C126are connected in series between the +15V supply line and ground, theresistor R258 being connected to the positive supply line, and themid-point of the bridge formed by R258 and C126 is connected to thecollector of Q100. The emitter of Q100 is connected to the -15V supplyline via a resistor R260, to pin 2 of U48 via a resistor R262 and to avideo output line 2568 via a resistor R264. To limit the outputpotential which can be placed on the line 2568, line 2568 is connectedto the anode of the first of a series of three Zener diodes, D100, D102and D104 all connected in series, D104 being connected to ground. Also,line 2568 is connected to the cathode of a Zener diode D 106, the anodeof which is grounded. Diodes D100, D102, D104 and D106 are all of thecommercially-available IN914 type. The video output line 2568 isconnected to the J7 connector of the AIM-65 mother board and is then fedto the video input of the video monitor 72 (FIG. 4).

The reader may have noted that one of the AND gates of integratedcircuit U7, two of the inverters of integrated circuit U14 and one ofthe inputs to integrated circuit U8 are not used in the above circuitry.In accordance with good circuit design practice, pins 1 and 2 of U7,pins 1 and 13 of U14 and pin 15 of U8 are all connected to the +5Vsupply line via a 1K resistor.

The circuits used to supply the necessary +5V supplies (connector J1,lines A, B, C, 1, 2 and 3) and the necessary grounds (connector J1,lines W, X, Y, 41, 42 and 43) are of the conventional types which willbe familiar to those skilled in the art and thus do not need to bedescribed in detail.

It will be apparent to those skilled in the art that numerous changesand modifications can be made in the preferred apparatus and the methodsof the invention described above without departing from the scope of theinvention. Accordingly, all of the foregoing description is to beconstrued in an illustrative and not in a limitative manner, the scopeof the invention being defined solely by the appended claims.

I claim:
 1. A method for illuminating a weld line to enable locating theweld line by an electronic video image detector, the methodcomprising:disposing a welding electrode adjacent a weld jointpreparation, said weld joint preparation comprising two metal portionsdisposed adjacent one another so as to define said weld linetherebetween; and directing a beam of light onto said electrode so as tocause part of said beam to be reflected from said electrode onto saidweld joint preparation, whereby an illuminated area is formed on saidweld joint preparation, said illuminated area traversing said weld lineand having an irregularity where said illuminated area crosses said weldline.
 2. Apparatus for illuminating a weld line for enabling electronicvideo image detecting of the weld line comprising:an electrode having anaxis, a tip and a sidewall, at least a portion of said sidewall beingcapable of reflecting light; and beam producing means for directing abeam of light onto said reflective portion of said sidewall, said beambeing directed at an acute angle to said axis and toward said tip suchthat said beam will be reflected from said reflective portion of saidsidewall so as to form an illuminated area on the surface of a workpiecelying adjacent said tip in a plane perpendicular to said axis.
 3. Amethod for illuminating a weld line to enable locating a weld line by anelectronic video image detector, the method comprising:disposing awelding electrode adjacent a weld joint preparation, said weld jointpreparation comprising two metal portions disposed adjacent one anotherso as to define said weld line therebetween; establishing alight-generating electrical arc between said electrode and said weldjoint preparation, said electrical arc not forming a molten pool on saidweld joint preparation, thereby causing light from said arc to bereflected from said weld joint preparation, said reflected lightdisplaying an irregularity at said weld line; receiving at least part ofsaid reflected light at a photodetector means; and analyzing saidreflected light received at said photodetector means to detect saidirregularity.
 4. Apparatus for detecting a weld line before the weldingoperation is commenced, the apparatus comprising:a welding electrode; apower supply means for supplying electrical power to said electrode formaintaining an electric arc between said electrode and a weld jointpreparation disposed adjacent thereto, the power supply means includingmeans for supplying a low power to the electrical arc which is less thanthe power necessary for forming a molten pool on said weld jointpreparation but emitting light; photodetector means for receiving lightemitted from said arc and reflected from said weld joint preparation;and analyzing means for analyzing said light received by saidphotodetector means and for detecting an irregularity in said lightindicative of a weld line on said weld joint preparation.
 5. A methodfor locating a weld line comprising:forming a pool of molten material ona weld joint preparation comprising two metal portions disposed adjacentone another so as to define said weld line therebetween, said pooltraversing said weld line, whereby a leading portion of said pool flowsbetween said two metal portions along said weld line, thereby causing aconcave distortion in the surface of said leading portion of said poolwhere said leading portion traverses said weld line; detecting lightreflected from said leading portion of said pool; and analyzing saiddetected light to detect a central local light minimum so as to detectsaid concave distortion and hence locate said weld line at the centrallight minimum.
 6. Apparatus for locating a weld line in a weld jointpreparation comprising two metal portions disposed adjacent one anotherso as to define said weld line therebetween, said apparatuscomprising:means for forming a pool of molten material on said weldjoint preparation, said pool traversing said weld line; photodetectormeans for detecting light reflected from at least a leading portion ofsaid pool, said leading portion having a concave distortion where ittraverses said weld line; and analyzer means for analyzing said detectedlight to detect a central local light minimum so as to detect saidconcave distortion and hence locate said weld line at the central lightminimum.